I'd get one of the nice socket AM2 motherboards. Yes the 939 boards are dropping like rocks in price, but have no upgrade path. No new cpu's are going to be made for them.

I'd look at Abit for the motherboard.
AMD X2 4400+ or higher for the cpu
At LEAST 1gb ram, 2gb if you can afford it.
Nvidia 790GS for the vid card around $200.
Western Digital 10k rpm hard drive.
NEC 3550A CD-RW/DVD+/-RW