for parts I would estimate between £1500-£2000.

Depends how extreme you want to go. Some parts are a bit overkill. But in general you would be looking at an SLi Motherboard, 2x 8800GTX cards (a bit overkill), Quad Core CPU (core 2 Duo), 4GB RAM (8 if you want and DDR3 if you want), about 900W+ PSU to run it all, A kick ass case like the Antec Gaming one, possibly watercooled, decent soundcard, dont know about hard drives. Thats about it really. DVD-RW and the rest are extras.