You definitely want to go for socket 939 and since they've released down to the 3000+ 64 I believe in socket 939 you should be able to get a good and fairly cheap Socket 939 system. I suggest you look into the 3000+ or 3200+ for Socket 939 if you're on somewhat of a budget.
Also the best motherboards IMO are the ABit AV8-3rd Eye and the MSI Neo2-Platinum, I've worked with the MSI, not the ABit, but ABit is a reputable company. The MSI board was good and has nice features and options in the BIOS, overall a good motherboard I say.
Also realize that we won't be in a 64bit environment until like 2006 so right now, since it's not fully utilized, if you can OC you can get a chip like mine and OC it to high speeds that'll surpass and AMD64 chip, but basically with the 64 you'll be setting yourself more up for the future in computers.