No question: Tyan Tiger 100. This is a solid entry level server
board. It's old school BX-based technology (UDMA33, 100Mhz FSB,
slot 1), but if you're gonna use PII 400's, what do you care.
No onboard SCSI, either, if that's important to you. Get a Revision
F of the board, and it'll support Coppermine processors as well,
if you decide to upgrade later on.
Kwad