Hey Scott welcome to the forums, i think you can do slightly better for your money:
Samsung SM-206BW 20" Widescreen LCD Monitor - Glossy Black
Microsoft Windows Vista Home Premium 64-Bit Edition DVD - OEM
Intel Core 2 Quad Pro Q6600 "LGA775 Kentsfield" 2.40GHz (1066FSB) - Retail
Abit IP35 Pro (Socket 775) PCI-Express DDR2 Motherboard
Crucial Ballistix 2GB (2x1GB) DDR2 PC2-5300C3 667MHz Dual Channel Kit X2
EVGA GeForce 8800 GTX 768MB GDDR3 HDTV/Dual DVI (PCI-Express)
Western Digital Caviar SE16 500GB 5000AAKS SATA-II 16MB Cache X2
Samsung SH-183LBEBN 18x18 DVD±RW Dual Layer Serial ATA Lightscribe ReWriter
Creative Sound Blaster X-Fi Xtreme Music 7.1 Soundcard - OEM
Corsair HX 620W ATX2.2 Modular SLI Compliant PSU
Akasa Eclipse 62 Aluminium Case - No PSU
Total : £1,475.58
Their you go.
I kept the same screen for you, very nice screen.
I have put Vista Home Premuium in their for you since i have also put 4GB of memory in the spec. So you will have to use a 64bit O/S to ultilize all of 4GB of RAM. You may not want to go over to Vista stright away but since you have 2, 500GB Hard Drives i would higly recomend Dual Booting XP and Vista.
This way you can experince Vista fully but if you do start to have problems you will still have XP.
The Quad Core you should be able to overclock it to 3 - 3.2GHZ without to many problems and with reasonable temps.
The Abit motherboard is one of the new P35 Chipsets, very reliable, rock solid, great overclocking boards. They also support Intels upcoming 45nm processors. Fantastic boards all around.
The Memory 4GB as i said earlier. Overclocking potenial of the Crucial Ballistix is brilliant. Will hit 1000MHZ+ pretty easily.
The GTX, fantastic card, you wont be disapointed.
2 Western Digital Hard Drives. Very fast and quite.
The Samsung DVD Writer, very nice drive. SATA connection so you can get rid of them ugle IDE cables.
Since this is for gaming i would higly recomend a Sound Card. The diffrence it makes as opposed to onboard sound is quite a bit. Well worth getting.
The Corsair PSU is one of the best PSUs around. Very solid and very quite. 850 watts is a bit of a overkill.
Now the Akasa case, the build quality is of a very high standard and the cooling is very very good as well.