If you get an Athlon-C and you get a DDR motherboard it will run at 133 FSB (266 Effective). The best motherboard for DDR right now is MSI's K7-Master-S. It's the motherboard Tom used in his Power Box. Unfortunatly, it is impossible to find so, I would for a DDR motherboard get either the Asus A7M266 or A7V266 (A7V266 has VIA's KT266 chipset isn't out yet).
I agree with looking at the Asus A7M266 motherboard, an Athlon C CPU to use the 133 MHz FSB, and memory recommendations. That will be my system early April. The 760 chipset is working best right now. Who really knows how well the KT266 will work?
Don't forget the MSI K7 Master (w/o SCSI) it much cheaper that the Master-S, if you can find it. Also MSI will be first to release a KT266 chip board with the MSI K7T266 Pro. Asus should be a close second with the A7V266. Im waiting to see what the picture looks like with them.
A revision to mpjesse's signature;
"My Signature Sucks"
im planning to buy a ddr utilitizing computer but i'm going to wait until more options become available and more bugs get fixed... personally... i think you should too