COuple of things, if you can save money somewhere else in the spec, go for an Nvidia 8800GT, it stomps all over both the cards youve chosen for not much more. If itll mainly be used for gaming Id suggest this card and a slightly slower cpu for overall better performance at the same price.
was looking at the 8800GT, but the reviews ive seen say stay clear of the 256Mb version because it isnt worth having, the 512Mb version adds at least £30 to the spec. Plus that also means swapping out the Motherbaord for a similarly specced SLi capable rig. Thatll bump the price again by 25-50 for a similar spec board. Another point, the 8800GT OC that ive seen a few places only beats the 3970 usually by 3-7 FPS. is it worth the £10 per-Frame it costs? Ive had difficulty finding a comparison between the Vanilla 8800GT and the 3870. Also a lot of the hardware sites are giving the 3870 "Best Buy" status in the price range because it is the best bang-for-buck.
Go for an E8200 Wolfdale on something like a Asus P5K-SE P35 mobo will save you a little on price. You only really need 2gb ram for gaming, if you want to scrimp a bit, then he can go for 6GB and a 64 bit OS later. The Wolfdales are the latest 45nm chips with an extra 2gb cache free.
We have a copy of XP64 already, hes refusing to use Vista at all because some of his specialist software isnt compatible unless he buys it again, but weve tested it under XP64 and it works fine. I was looking at the Wolfdales, but once again Intel have paper launched the things, everyone has prices, but hardly anyone has stock. Plus guy wants the ability to drop crossfire or SLi into the mix at a later date, so we have to have something that is capable of it.