Asrock 775Dual-VSTA can use 2 slots of either.
Many, many ppl have bought this board, and the only "complaint" I here is the very limited OC'ing, and the limit to 2 memory slots.
DDR400 on this board holds it's own quite well against DDR2. In fact, I think it was anandtech itself that showed benchmarks where the DDR-400 would beat DDR2-533. It was only until DDR2-667 that benchmarks started showing a difference.
(Partially had something to do with memory/cpu ratios, since 1:1 is optimal. Other websites have also shown there is little to no performance hit in going DDR over DDR2).
DDR2 has options for faster RAM, and is much more future proof - but you get what you pay for.
I'd check the thread on this mb on this website.