it maybe worth looking at a HX520 rather then a HX620, as the 520 will easily power that PC, otehrwise it looks like a very good spec for gaming. look into getting better audio equipment if you want/need.
edit, a spec.
it is nearly idential to yours, iwth a few small changes
Your basket
Product Name Qty Price Line Total
Abit IP35 Pro (Socket 775) PCI-Express DDR2 Motherboard £101.99
(£119.84) £101.99
(£119.84)
OCZ 4GB (2x2GB) PC2-6400C5 Dual Channel Vista Gold Series DDR2 (OCZ2G8004GK) £49.99
(£58.74) £49.99
(£58.74)
Antec Nine Hundred Ultimate Gaming Case £61.99
(£72.84) £61.99
(£72.84)
Intel Core 2 Quad Pro Q6600 "Energy Efficient SLACR 95W Edition" 2.40GHz (1066FSB) - Retail £144.99
(£170.36) £144.99
(£170.36)
Tuniq Tower 120-LFB CPU Cooler (Socket 478/754/939/940/AM2/LGA775) £22.99
(£27.01) £22.99
(£27.01)
Arctic Silver 5 Thermal Compound (3.5g) £5.99
(£7.04) £5.99
(£7.04)
Western Digital Caviar SE16 500GB SATA-II 16MB Cache - OEM (WD5000AAKS) £54.99
(£64.61) £54.99
(£64.61)
Corsair HX 520W ATX2.2 Modular SLI Compliant PSU (CMPSU-520HXUK) £59.99
(£70.49) £59.99
(£70.49)
OcUK GeForce 8800 GT 512MB GDDR3 HDTV/Dual DVI (PCI-Express) - Retail £139.99
(£164.49) £139.99
(£164.49)
Sub Total : £642.91
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(This can be changed during checkout) Shipping : £12.95
VAT is being charged at 17.5% VAT : £114.78
Total : £770.64
i put a hx520 in as i know its powerful enough. most people overestimate the power consumsion of their Pc.
i opted fro pc2-6400 ram, as this will allow you to have a FSB of 400MHz before your RAM will need Ocing, the q6600 has a multiplier range of between 6-9, your cpu clock speed is basicly the FSBxmultiplier, in simple terms. you also have 4GB of RAM here rather then 2GB. your maximum OC, before your will need to be OC'ed using the highest multiplier is 3.6GHz.