Athlon XPs use Socket A (aka Socket 468.)
For a 32-bit AMD platform, the best boards out there are those with the nForce2 chipset, namely the ones that mention the Ultra400 set, with the MCP-T northbridge.
If you don't get one with MCP-T, you miss out on kick-*** audio that rivals an Audigy2, and possibly dual-channel memory and S-ATA support, though i'm not sure on those last two.
The companies that make the best nForce2 boards, as far as I know, are DFI, Gigabyte, and Asus.
for pricing and availability.
Leadtek and FIC have always made solid boards too, so don't count them out.