looks good to me except I might opt for a 2800 as you can get one from newegg for 109$, the 3000 is 50% more cost but only 200 more pr points! so the best bang for the dollar is the amd64 2800. Its all up to yiou guys though. Then i'd get cheaper ram amd put the savings into the video card as that is what will really supercharge the system.
btw the pr points and stuff are decieving a bit... the amd64 2800 will blow away the xp 2800 in everything especially games and memory intensive applications.
supernade's idea would give you the best performance for the dollar though.
To tell you the honest truth, you could probably get a PCI express nvidia 6600 or 6200 cheaper than a AGP version, so if you did go the socket 939 route,
amd64 939 3000= 150$
ECS nforce 4 board =76$
leadtek geforce 6600 = 109$
cheapo case w psu= 40$
512mb geil value 2X256= 57$
dvd burner =50
hard drive=80
562$