AMD Athlon 64 X2 Dual Core 4200+ 2.20GHz (Socket AM2) - Retail
£51.69 inc VAT
Asus M2V (Socket AM2) PCI-Express DDR2 Motherboard
£41.11 inc VAT
Corsair 1GB DDR2 XMS2-6400C5 TwinX (2x512MB)
£37.59 inc VAT
OcUK GeForce 7600 GT 256MB GDDR3 TV-Out/DVI (PCI-Express) - Retail
£58.74 inc VAT
OCZ GameXStream 600w Silent SLI Ready ATX2 Power Supply
£58.74 inc VAT
Creative Sound Blaster Audigy SE 7.1 Sound Card - OEM
£16.44 inc VAT
OcUK Value Hanns-G HC194D 19" LCD Monitor - Silver/Black
£99.86 inc VAT
Total of £364.17 so far, with remaining 105.83 to spend on a Case, Hard Drive, Optical Drive, keyboard and mouse. Haven't picked these for you because i don't know if you have any spares or not. Graphics card you can change to a cheaper one if you wish, same with the processor.
Hope that helps