it was just a quick once over as I'm in work there's plenty of other sites to find cheaper parts I'm sure my build isn't the best. He could try searching the following:
Went for an AM2 setup gives you more chance to upgrade in future. Added a case and PSU to the list had originally thought you wouldn't need them as you have monitor, old case etc.
I squeezed the best setup I could for £570 lol . Although I do think the setup is worth every penny i got the 7600GT and a dual core AMD in your setup . Now to get to £500 lol a few options get the hard drive you want only 80 gigs lower the graphics card down, or go single core... I tried my best, guess you could go for an AMD 3700+ or something lower all your expectations, the PSU and case really kill the deal shame you cant use your old one. You could also buy a case PSU combo its cheaper but nasty your choice.