Me and my brother have identical (3+ year old) systems:

MSI K8T Neo FSR
AMD Athlon 64 3400+
1GB of Ram
Geforce 6800
Creative SB Audigy 4

Recently both of our MSI K8T mobos died and I'm unable to find replacements motherboard that supports the agp gpu, 754 socket cpu, etc. So it looks like I'll need to some upgrading. I want parts that are the best bang for the dollar, but not top of the line, I want to keep the total under 500 if possible (don't have a ton of money to throw around). I have no interest in SLI, I do not overclock. My brother uses his system mostly for games such as World of Warcraft, I use mine for programs like photoshop.

So far I've been looking at:

AMD Athlon 64 X2 6400+
http://www.newegg.com/Product/Prod [...] 6819103228

I thought about Intel's 8200 or 8400 wolfdales, but are they really that much faster than the 6400+ if you don't plan to overclock?

MSI NX8800GT 512M OC GeForce 8800GT 512MB
http://www.newegg.com/Product/Prod [...] 6814127329

I also need the motherboard and memory, Sharkyextreme's guide recommends the Gigabyte GA-MA790X-DS4 (AMD 790X). I haven't seem very high reviews on this board though. I randomly was looking at boards and found this one had a lot of good reviews;

http://www.newegg.com/Product/Prod [...] 6813131013
ASUS M2N-SLI Deluxe AM2 NVIDIA nForce 570 SLI MCP

The thing is, I really don't know that much about motherboards, and what to look for, I know I won't be using sli though. Basically I just want a stable motherboard. I'm not sure about how much ram to get. I will probably only use WinXp. I realize Winxp will only see like 3gb of 4gb of ram, will that 1gb make much difference over 2gb? Lastly, will 450 Watt PSU be enough? Anyway, I really appreciate the help. If you could help me figure out which motherboard to get I will really appreciate it.

don't get the amd6400, get the 5000be instead and overclock. overclocking this processor is easy since it has an unlocked multiplier. plus it's way cheaper.
http://www.newegg.com/Product/Prod [...] 6819103194


get 2gb of ram. ram is cheap so buy as much as you can. 2gb dual channel ddr2 800 kits you can find for about 50 bucks, even cheaper with rebates.

450watts should be enough, as long as you have a good brand name psu not some crappy one.

mobo? i have msi k9a2 platinum. it supports all of amd processors, plus i find it very stable. i overclock all the time and it's stable. i think it costs 150 at newegg. maybe someone else has a suggestion for a cheaper one with different chipset.

Ok.. you have no interest in SLI. No point in buying a SLI motherboard.

Let's talk about this build piece by piece.

CPU: 5000be for sure
Video: One you choose is fine, but this one will save you $10
http://www.newegg.com/Product/Prod [...] 6814150280
Motherboard: Save $30 and use this one instead:
http://www.newegg.com/Product/Prod [...] 6813131289
RAM: 2GB and get this kit: only $50 and its 4-4-4-12:
http://www.newegg.com/Product/Prod [...] 6820231087

Case/PSU: Antec Sonta III $100 after rebate w/ free ship
http://www.newegg.com/Product/Prod [...] onta%2bIII

Ok, so I'm looking now at this mobo/cup;

Intel Core 2 Duo E8400 Wolfdale 3.0GHz 6MB L2 Cache LGA 775 65W Dual-Core Processor
http://www.newegg.com/Product/Prod [...] 6819115037

which is 30 more than the 6400+, but the motherboard's price would make up for that, and the 8400 got much higher numbers in benchmarks I saw

GIGABYTE GA-EP35-DS3L LGA 775 Intel P35 ATX Intel Motherboard
http://www.newegg.com/Product/Prod [...] -EP35-DS3L


Ram I'm looking at:

CORSAIR 4GB (2 x 2GB) 240-Pin DDR2 SDRAM DDR2 800 (PC2 6400) Dual Channel Kit Desktop Memory
http://www.newegg.com/Product/Prod [...] 6820145184

or

2gb version of above
http://www.newegg.com/Product/Prod [...] 6820145034

or

OCZ Reaper HPC Edition 4GB (2 x 2GB) 240-Pin DDR2 SDRAM DDR2 800 (PC2 6400)
http://www.newegg.com/Product/Prod [...] 6820227267

2gb version of above
http://www.newegg.com/Product/Prod [...] 6820227231

I'm leaning towards the $68 OCZ which has lower timings than the corsair. The problem is, I really don't know the benefits. Is there a noticeable difference between the 4-4-4-15 and 5-5-5-18? Also, I may end up getting the 4gb even though I have no real reason to. For memory intensive games like world of warcraft, will 4gb of ram have any difference? If not, maybe I will get 2gb

For WoW and the vast majority of applications, 4GB of RAM will not make any difference. For video editing, photo editing with PS and other such activities it WILL make a difference.

That motherboard does not overclock very well, if you read the comments. Not sure if that is important to you or not.

I think you have made excellent choices. the E8400 CPU and Gigabyte GA-EP35-DS3L motherboard are very good. The user reported overclocking problems I read about were really not overclocking problems - the users had not turned off the energy savings features that were lowering speed of the processor - but only when speed was not needed - such as when they were only checking speed on CPU,

Both Corsair and OCZ make good memory. I beleive the Corsair XMS memory is on the approved list for the motherboard - did you check?

You might consider getting 2x1GB for the gaming system and 4x1GB for the photoshop system, then spend a little more on the graphics card for the gaming system.