I've been thinking about my new system which i'm planning to build and this is what i've narrowed some bits of it down but i still need some help/advice as i'm quite new to the new hardware's (last time i upgraded my pc was 3-4yrs back)
 
(hardware pieces are all from local market, i'm not planning on doing anything online, also all prices listed are about 2 weeks old (relevance???? ))
 
Case: no idea yet, still have to see what's available and also doesn't the size of the case depend on the components inside?
 
Power supply: no idea either but i guess it should be over 1000W (you'll see why below)
 
Motherboard: ASUS ....actually nope i don't have an idea either here but please do recommend me ones that will be suitable and good according to the other parts
 
Processor: decided on quad-core for sure
 
AMD Quad Core Phenom 9850 BlackEdition 2.5Ghz (AED945 ~ $257)
 
or
 
Intel Quad Core Q9300 2.5Ghz (AED1035 ~ $282)
 
Last time i checked they didn't have the intel quad cores 2.66ghz but they're available next time i check i might think of getting it, considering the price ofcourse. HOWEVER, which of the 2 mentioned (AMD 9850BE and Intel Q9300) is better in performance and overclock-ability?
(AMD's are usually less pricey than Intel's due to the price system over here being after brand names)
 
 
Graphics Card:
 
Nvidia GTX280 (AED2600 ~ $708)
 
or
 
ATI Radeon HD4870 (AED1200 ~ $326)
 
The GTX280 price was before the decrease nvidia was planning as mentioned on tomshardware but i'm not sure if they decrease the prices here as well...so anyways
 
The price of 2 4870's will cost almost as much as the GTX280 so if i'll be going for the 4870 i'm planning on getting 2 and crossfire them but if i'm going for the gtx280 i'll be getting just one.
But which is better? I've read some of the benchmarks (didn't really understand much) and both cards seem to be outstanding. Which is more advisable to get the gtx280 or 2 4870's or even just one 4870 ?  
 
Also regarding the card's memory. The GTX280 uses GDDR3 and the HD4870 uses GDDR5. Does this have any implication on the type of desktop RAM? or anything else?
 
Hard Disks: i don't really think its important but a 250GB is AED180 (~$49)....is there anything special i should be looking out for ?
 
RAM: 2GB Corsair DDR2 is AED185 ~ $50
 
My OS will be Windows VISTA (yuck) Ultimate edition or home premium, does VISTA require more than 2GB and is it advisable to get more for gaming, etc??
 
Optical Drive: i'll be using the same one installed in my current pc, LG DVD writer.. hardly use it

I have seen your whole configuration and it is good and I wiil advice to go with  
 
Intel Quad Core Q9300 2.5Ghz (AED1035 ~ $282)  
and for windows Vista  ultimate 2GB is sufficient, but if you go for 4 GB you will get enhanced performance.

there is really no need for a 1kw psu, 750-850 should suit you well
 
and why not from online? there's a bigger variety, and prices are usually lower

You won't need a 1000W PSU.  For a single card, even the high-end ones, 650W should be sufficient (a quality 550W would probably work, but leave little cushion).  If you Crossfire two 4870s, even then 850W is sufficient.
Intel chips tend to overclock better than AMD, blowing them away on performance.  You'd probably only want AMD if you are certain you won't overclock, and are on a tight budget.  Since you're looking at high-end graphics cards, I'm "guessing" that Intel will be the better choice for you.
In your place, I would buy a single 4870, and a motherboard that would allow me to add another one later if I absolutely needed it; if I wanted to save money, I'd forego Crossfire entirely.
Case appearance is entirely a matter of personal style, but make sure it has good airflow.  I personally like CoolerMaster cases, as even the lowest-price ones have places to mount front and rear fans, and they have tool-free drive mounting.

I'm currently running vista ultimate 32 bit with 2gb of ram and would definitely recommend going for more...
And about the gpu, I agree with jtt283...get a single 4870 with a 790FX mobo....then when you need to, add the other for crossfire...(although I've heard that the current stage of two 4870's crossfired is about equal to the same performance of two 4850's crossfired...but I'm guessing this will change with newer drivers...)

spend the extra money and get 4gb (2x2) of RAM.  Vista is actually a great OS but it definately likes memory. Get Home Premium x64.
 
I would also recommend that you spend a little more (approx $60) and get the Q9450.  Other than the increased clock speed you increase the FSB mem from 6mb (shared) to 12mb (shared).  If you are going to be using this for any type of video editing the increased FSB mem will help, substantially.  If not then you might as well get the Core 2 Duo for $100 less.
 
HDD - I was actually very surprised with how much my new HD helped my system.  I went from a 2 year old 7200 RPM to a new Seagate 7200.11 (500GB) and there is definately a noticeable difference in performance.  For example, I play BF2 and with my old system I loaded moderately fast but not fast enough to be one of the first in.  With the new HD I am always the first in.  Other than that my comps boot time was basically cut in half.
 
Case - my preference is the Antec 900 but as long as the case you chose has good airflow it should work fine.

My recommendations:

Q6600 or E8400 (E8400 if doing gaming mostly; else get the quad)
ATI 4870 (see how one card dose first, then decide on if to CrossFire)
P45-DS3R or P45-P5Q Pro
2*2GB DDR2 800
PP&C 750 or Corsair 750TX (if doing CrossFire); else a PP&C 610.
500GB+ 7200.11 HDD(s) possibly in RAID.
Vista x64

Case is a personal choice, but I recommend Antec 900.

If OCing: XIGMATEK S1283.

The Intel will be easier to OC and will OC better than the AMD.  
 

The 2* 4870 in CrossFire will be better than the single GTX280
 

thanks for the input guys...but it seems that most of people are trying to stay away from the GTX280 and are leaning towards the 4870 might i ask why? i'm not in preference of any they both seem to be amazing cards
also what i'm worried about is the 4870X2 which is rumored to be released on August (this year?) and i'm thinking if it is advisable to get the 4870 or the 280 on this regard?
 
@eklipz330 well i know that online purchasing gives me a wider variety but first i don't want to wait , second i don't have that much experience on online shopping and it's not that common over here and lastly i really dont like waiting for the parts to arrive

one additional question is it possible to crossfire a single 4870 with the new upcoming 4870X2 ?

i went to newegg and checked out the motherboards on sale but i didn't know what i should be looking for based on my other proposed parts?

the initial answer to your xfire question is no.  That does not mean it won't change etc but so far both manufacturers only allow xfire/sli to be done with identical cards.
 
if you are oging to get a 4870 then I would highly recommend the X38/X48 chipset for your motherboard.  The intel chipsets (X38, X48, P35, P45 etc) support crossfire(all ATI GPU's).  The nvidia chipsets (680i, 780, 790 etc) support nividia's SLI (all nvidia GPU's).  
 
The reason you are seeing most people recommend the 4870 over the nvidia card is simply based on the price vs. performance.  The nvidia 280 is inarguably the most powerful card on the market but it is also the most expensive, by a wide margin.  You can still get a 4870 for $200 less then the 280.  Add to that the fact that the only time you might need the extra performance is if you are playing Crysis with all settings on high,  4xAA and a resolution of 2500 x 1600.  Other then that the 4870 will easily run any game on the market.  I would even be comfortable recommending you use the 4850 in crossfire over a single 4870 or 280.  read the attached article before making your GPU choice.
http://www.tomshardware.com/review [...] 965-4.html

the motherboard prices are high i never knew motherboards got as expensive as they are
just out of curiosity is there any motherboard that is compatible with both ATI and Nvidia in CrossFire and SLI?

i cant seem to edit my messages?
 
i just wanted to mention that i'm not planning on getting a sound card an onboard one is good for me

 
 
 
No.  It's not that it's impossible.  It is just one of those licensing (the 2 big kids don't play well together) things.

Yes, you will need to buy a Skulltrail for that.

i've narrowed the motherboards further down in the case of CROSSFIRE with ati cards to either X38 or X48. (for sli-ing, still researching)
does the motherboard have to say its crossfire compatible/supported for crossfiring or it's not necessary?
Also another question about motherboards, if it says "memory standard: DDR3" is it backwards compatible? i.e if i put a DDR2 800 RAM stick would it work?

motherboards are not backward compatible so make sure you get one that is built for DDR2. DDR3 is overpriced at the moment and offers very small gains in performance.  
There is 1 board (maybe more now) that can use either DDR2 or DDR3.  If you get that you will be limiting yourself to 2 memory slots for each.  
I have not seen an X38/48 board that does not support xfire but...  If you have a question check the manufacturers web site.  I would recommend one of the following boards.
ASUS P5E LGA 775 Intel X38 ATX Intel Motherboard
http://www.newegg.com/Product/Prod [...] 6813131219
GIGABYTE GA-X48-DS4 LGA 775 Intel X48 ATX Intel Motherboard
http://www.newegg.com/Product/Prod [...] 6813128336
 
I know you cannot use newegg but this is just meant to be used as a reference.