You are not going to be able to build a good Intel computer for that budget. The CPUs Intel makes that would be in your range are underpowered compared to AMD's lines. In addition, the AMD build would be more upgradeable. Look at AM3 socket CPUS.
I would also check out the ATI video cards. They're newer, better and cheaper.
For the motherboard, look for ones with DDR3 RAM. This is newer and faster, and is coming into common usage. DDR2 is on its way out and will be hard to find if you upgrade or expand.
I'd check around for some different RAM. I'm not sure on prices in England, but here in the US Corsair memory is a lot more expensive for not getting a whole lot more. You can probably find some CAS Latency 7 DDR3 sticks for the same price (or cheaper). This would be faster than what you've got. Check out some G.Skill Ripjaws or OCZ.