If you want a dual-processor Pentium4 system, the Xeon proper is what you're after. Xeons are dual-capable. If you're after a mobo that'll do dual Xeons without requireing a monster server chassis and EPS power supply, look at the Asus PC-DL Deluxe.
link to PC-DL Deluxe and some other dual-Xeon boards
Be aware that a single Pentium4 3.2C would be a faster gaming rig than, say, dual Xeon 2.8's, if all you're into is gaming. Don't buy this without knowing what it can and cannot do for you

If you want to equip it with 2GB+ of RAM and play high-end games while simultaneously doing a 4-hour video-encoding session, NOW you will reap the benefits of a dualie. But you could probably build a second single-processor system to do those secondary tasks for less money.