I've been asked to put together a budget gaming PC for a family member, as a birthday present due in a month or two. The recipient currently has a low end 2.4 GHz Celeron box with 1GB of RAM and an old GeForce 4 MX graphics card. He plays games like Age of Empires 3, Wesnoth, etc. but would be interested in more modern stuff like Call of Duty: World at War.

The budget is £250-£300 with emphesis on the lower end. I'm thinking along the lines of:
Intel Core 2 Duo E7400 or AMD X2 7750 (much cheaper)
2-4GB RAM
nVidia GeForce 8-series card like a 8800GT
Motherboard
PSU

I'd re-use the optical drives and hard disk from his current machine. At a first glance I think the budget is going to be tricky to meet. I don't really play PC games these days so don't know where not to skimp. Any ideas?