P4's, properly speaking, aren't dual-capable. The Xeons are derived from the P4 core, but use different sockets. What the best motherboard is for dual Xeons will depend on what you're after. Some of the "best" ones have no AGP slot, for instance (they're server boards in the $500+ range) and almost all Xeon boards are dualies, period, starting around $350 (I did see one ~$280 single-CPU Xeon board).