If i were you, i'd start a fresh build: (all products from
Computer hardware and software at amazing prices, available online from Scan Computers UK)
LN17776 - Asus TM-210 Black/Silver MicroATX Case w/o PSU £24.57
LN21476 - 512MB Palit/XVision 8600GT, PCI-E (x16), GDDR2, 2xDual Link DVI-I/HDTV £42.88
LN11596 - 2GB (2x1GB) Corsair TwinX XMS2, DDR2 PC2-6400 (800), 240 Pins, Non-ECC Unbuffered, CAS 5-5-5-12 £28.95
LN21757 - Gigabyte GA-P35-S3G, iP35 Express, S 775, PCI-E (x16), DDR2 1066/667/800 MHz, SATA II, ATX £51.69
LN19492 - 450W Corsair VX Series PSU, ATX, PS/2, UK Version, 80 PLUS® certified £44.05
LN19277 - Intel Core 2 Duo E4500, Allendale Core, S775, 2.2 GHz, 800MHz FSB, 2MB Cache, Retail
It comes to £280 including postage and I haven't included monitor, hdd, operating system, keyboard, mouse and optical drive.
you don't need an 8800GT for a 17" monitor, 8600 is fine. (i've got a 17" monitor that can run off a GS 5400 - or something like that )
i've included a good motherboard that you can have lots of fun overclocking with