First Time Builder, please Help lads - Which MOBO?

Hi there Guys, I'm a complete noob, struggling with the ridiculous amount of choice as far as components are concerned -i'm going to build a pc from scratch for:
Gaming
Excel formulas and Market calculations
Translating

So I opted to go for a slick system. So far i'm thinking of the following components, but I'm not sure if they're going to mesh well together into a motherboard, let alone which one.....They are:

Intel Core 2 Quad Q9450 2.66GHz 12M Cache processor
4870HD GPU
Dual monitors
Akasa 850W AK-P085FG-BK PowerMax PSU
Then either 4GB DDR3 or 8GB DDR2

I thought the most difficult things when considering teh mobo were the DDR3, 4870 and the monitors.
I also want to get a relatively good mobo for future proof reasons
Budget about £1,200 ($2,400)
Can you give me some suggestions please guys?
Thanks!

1 x ANTEC - P182 SE Advanced Super Mid Tower, Stainless Steel Mirror Finish ( $179.95 )

1 x Intel - Core™2 Quad Processor Q9450 2.66GHz w/ 12MB Cache ( $369.95 ) Get OEM... save a few bucks.

1 x ARCTIC SILVER - Ceramique Premium High-Density Thermal Compund, 2.5g ( $8.49 )

1 x Arctic Cooling - Freezer 7 Pro CPU Cooler for P4/775 ( $29.95 )

1 x Gigabyte - GA-X48-DS4 w/ DualDDR2 1200, 7.1 Audio, Dual GB Lan, 1394, Dual PCI-E x16 CrossFire ( $259.95 )

1 x Corsair - 4GB XMS2-8500D Dominator TWIN2X Dual Channel DDR2 Kit (2 x 2GB) w/ Airflow Fan ( $179.95 )

2 x SEAGATE - 500GB Barracuda 7200.11 SATA II w/ NCQ, 32MB Cache ( $149.90 )

2 x LG - Super Multi Security DVD Writer 20x20x10 w/ Lightscribe, Black (OEM) ( $69.90 )

2 x SAPPHIRE - Radeon HD 4870 512MB GDDR5 PCI-E w/ Dual DVI, HDTV-Out, HDMI ( $639.90 )

1 x PC Power & Cooling - Silencer 750 Quad Power Supply, Crossfire Edition ( $159.95 )

1 x Microsoft - Windows XP Professional w/ SP3, OEM ( $145.95 )


Total $2,193 + tax

Case
Antec Three Hundred Ultimate Gaming Case
£35.24

Processor
Intel Core 2 Quad Q9450 LGA775 'Yorkfield' 2.66GHz 12MB-cache (1333FSB) Processor
£206.79

Motherboard
Asus P5Q-E Intel P45 (Socket 775) PCI-Express DDR2 Motherboard
£99.86

Graphics card
Sapphire ATI Radeon HD 4870 512MB GDDR5 TV-Out/Dual DVI/HDMI (PCI-Express) - Retail
£154.99

RAM
Corsair 4GB DDR2 XMS2 PC2-6400C5 TwinX (2x2GB) times 2
£64.61

PSU
Corsair HX 520W ATX2.2 Modular SLI Compliant PSU (CMPSU-520HXUK)
£70.49

2 Auxiliary 120mm fans
Arctic Cooling Arctic Fan 12PWM 120mm Fan - 4-Pin PWM
£18.78

Optical Drive(s)
Samsung SH-S223F/BEBE 22x DVD±RW SATA Dual Layer ReWriter (Black) - OEM
£17.61

HDD
Seagate Barracuda 7200.10 250GB SATA-II 16MB Cache
£34.06

2nd HDD
Western Digital Raptor 74GB 10000RPM SATA 16MB Cache - OEM (WD740ADFD)
£92.81

Monitor
Samsung SyncMaster 2253BW 22" LCD Monitor times 2
£151.53

Total
£1,127.67

Thanks guys you are both clearly clued up , a couple of questions though:

1. Shall I get a MOBO that will be able to support DDR3 when it finally improves?
2. I assume the MOBO will be able to handle the 2 monitors right?
3. Evongugg - If i want to run my HDs on RAID, do they have to be the same? Want RAID for speed basically!

thanks!!

evongugg..
1) Raptors are old school and not needed anymore
2) 7200.11 HDD's are prefered over 7200.10
3) add $ for an OS, he wants Vista..