Why not get a duallie board, but only use one socket? I'm fairly sure you can do this - although server stuff isn't really my thing, so I could be wrong.
I doubt a single socket board will be substantially cheaper (if one exists).
Epox 8RDA+ rev1.1 w/ Custom NB HS
XP1700+ @205x11 (~2.26Ghz), 1.575Vcore
2x256Mb Corsair PC3200LL 2-2-2-4
Sapphire 9800Pro 420/744