Right this is what i've managed to come up with for my brothers i5 build
MSI GD80 - £85.50
Core i5 750 - £145.48
G.Skill Ripjaw 4GB (2x2GB) DDR3 PC3-12800C9 1600MHz Dual Channel Kit - £59.11
Coolermaster Elite 335 - £25.29
OCZ ModXStream Pro 500w - £50.19
Western Digital Caviar Black 500GB - £41.59
Samsung SH-S223B/BEBE - £15.15
XFX HD 4850 XXX Edition 512MB - £79.90
Grand total of £502.21 give or take a few discounts!
The main thing I am unsure about is the case and have been looking at the Antec Three hundred (on dabs for just under £40)
Any further recommendations appreciated and apologies for keep clutting up the forum!