Do not get the A7V, its stable pretty stable, but there are much better out there. SDRAM is not the way to go also, especially with an XP CPU, you are setting up a major major bottleneck.
For stability, 760 is the best, imo, the FIC AD11, but it won't take a XP, or at least the first generation won't, maybe another revision will. Most 760 boards are very very stable, epox for sure, I'd stay away from the Asus board, as it was realeased far ahead of most other boards. Abit has a good 760 board too.
KT266A is extremely stable, or most boards are too. I love my KT266A board, I'd use it as a server if I wanted to.