OK....thought about it and decided to spend a bit more money, took bits of what you have suggested and came up with the below, slightly beefed up the CPU/Motherboard, extra 2gb and a GT card, is the gigabyte OC one any good?
Hows the below look and do you think it would all fit into a Lian-Li PC-7, that Tuniq looks like a big mother of a heatsink!
Below comes out at £744.76 including shipping, just £144 over my original budget
Intel Core 2 Quad Pro Q6600 "Energy Efficient SLACR 95W Edition" 2.40GHz (1066FSB) - OEM (£152.74) £129.99
Corsair 4GB DDR2 XMS2 PC2-6400C5 TwinX (2x2GB) Corsair 4GB DDR2 XMS2 PC2-6400C5 TwinX (2x2GB) (£76.36) £64.99
Western Digital Caviar SE16 500GB SATA-II 16MB Cache - OEM (WD5000AAKS) (£64.61) £54.99
Arctic Silver 5 Thermal Compound (3.5g) Arctic Silver 5 Thermal Compound (3.5g) (£7.04) £5.99
Corsair HX 520W ATX2.2 Modular SLI Compliant PSU (CMPSU-520HXUK) (£70.49) £59.99
Gigabyte GA-P35C-DS3R (Socket 775) PCI-Express DDR2 & DDR3 Motherboard (£82.24) £69.99
Gigabyte GeForce 8800 GT OC 512MB GDDR3 HDTV/Dual DVI (PCI-Express) - Retail (GV-NX88T512HP)
(£158.61) £134.99
Lian-Li PC-7 PLUS II Aluminium Midi-Tower Case - BlacK (£58.74) £49.99
Tuniq Tower 120-LFB CPU Cooler (Socket 478/754/939/940/AM2/LGA775) (£35.24) £29.99
Scythe S-FLEX 1600RPM Ultra Quiet 120mm Fan - 3/4 Pin (£12.91) £21.98