Not saying you should do this, but you could build something for half that cost that would be only slightly slower. Are you going to be happy when, in 3 months' time, this will be slower than the Yorkfields/Agenas and 8900gtx's/x2900xtx's which will probably be out by then?
Why not get something that will run games at about 90% the framerate, but will cost half? i.e. a P5B Deluxe mobo, an e6400 (do you need quad? Why?), one 8800gtx (SLi often shows little or no performance benefit, e.g. Half Life: Lost Coast, so why spend an extra £400?), 2gb of decent value ddr2-800 ram, 1 raptor, and a 520w corsair psu.
Like I say, just an idea.
EDIT: I should say that this assumes you will overclock, and you will need a decent cooler, such as the Tuniq Tower 120 (+ a nice 129mm fan, such as Scythe S-Flex). You can OC to 3.2ghz with ease.
What monitor and case are you thinking of getting?
You CAN pay that much money, but if you want a motherboard with the same features but less bling, you can have the Evga 680i for almost half the price.
Unless you're going to overclock, DDR2 800 RAM is cheaper. You could probably get even 667 or 533 and save even more money.
This looks like a gaming machine, so why handicap yourself with Vista? I'd wait until Vista SP1 before I go there. Vista still has a ton of driver issues and doesn't play well with a lot of games out there. But if you like adventure, then Vista's your thing. I would stick with XP.
Have you thought about a case? Check out the Thermaltake Armor - great case, lots of room.
Get an after-market cooler like the Tuniq Tower 120 or the Scythe Infinity. Depending on how much of a hastle you like to go through, I'd go with the Infinity. The Tuniq is the best air cooler you can get, but it's a major PITA to get it to sit right.
I have updated my recommendations for a new Rig I think you can also get an Idea of the best values in the Market.
(I wrote it for my Guild)
Mother Board DFI Infinity 975G/X at only $160 this board is a steel.
I've read up on this board extensivly and have read about pep's run SLI on it. I've got mine to run 400X9=3.6GHz Orthos stable @390X9=3.5 GHz 1.45 V
If you opt for a less expensive C.P.U. you should pair that with a 965 Chip set that can do higher Front Side Buss. Like this Gigabyte-Gigabyte-GA-965P-S3-P965-Express at $120 is a great buy as well.
C.P.U. Intel Core 2 Duo E6600 Get all the amenities of the $1000 Chip then Over Clock it way past it's Extreme Brother at $316 How can you beat it.
Hard Drive Seagate 7200.10 Perpendicular Drive With 16 MB Cache almost as fast as a Raptor and 320 GB all for only $95
Memory really any 800 MHz DDR II RAM Will Do as the processor only needs 533 Mhz to Run at 1:1 there is a lot of head room in DDR2-800. I think the actual Integrated Circuits on the DIMMs are more important than the speed of the DIMMS. Micron Rules and I've head pep's bragging about PROMOS. Two 1 GB Sticks are recommended. $230
Power Supply Seasonic M12 it's like my 600 Watt S12 but modular.$150
Graphics Card EVGA 8800 GTS 640 MB ya I like mine and have a hard time recommending a $600 Card.$400
I really Like Zalman for CPU and GPU Coolers I'd Like to try the 9700. My 9500 is running 63C at full Duel Load so I'd appreciate the double in surface area of the 9700. $60
I Like 20X Lite-On Light Scribe DVD/RW Drives I reccommend the Retail box from Newegg as it give you Nero and Power DVD 6 for $37
Case Antec 900 It has Gread Air Flow.
I have all most of thses components but not all in the same System
So $1606 in Hardware
Windows XP Media Center Edition 2005 For $130
=$1,736 +$250-$300 for a Nice L.C.D. and you got a Killer Gameing Rig for $2K!
I'm running 3.5 GHz Orthos Stable I acheaved a 10800 3D Mark 06 Score.