There is a whole heap of newer Xeon boards coming out (check )
2CPU.com for more info and reviews). Problem is, they're not cheap (neither are the Xeon CPUs for that matter) and they're huge mobos! Won't fit in your Lian-Li PC-65, for example.
Moreover, they don't really outperform dual Athlon MP boards, even with hyperthreading enabled, in any significant way (and to get HT you're looking at W2000 server edition as Microsod has limited the licence on other Windows to only "see" 2 logical processors rather than 4). The Athlon setup will be about $2000,-- cheaper and just as fast and reliable, really...
Makes you wonder why AMD doesn't focus more on the MP market, where they definitely have the competitive edge, instead of trying to make the XP keep up with the P4. No wonder the company's struggling.