One of the cheapest dual cpu mobo available at the moment is the Tyan TigerMP; which doesn't have any special PSU requirements, but does, as with all other dual AMD boards, demand sufficient power on the 5v line.
I'd urge you to check out the
www.2cpu.com site, and especially the forums, to answer any and all of your questions. Thousands of hours of reading and very educated users - most of whom are more than happy to give excellent detailed advice on this tricky subject.
I built my system back in Feb this year, using the TigerMP and two XP1800+ processors; both of which were smp "unlocked", so I popped them in and they worked exactly as if they were the "MP" processors. Now though, most (all?) XP processors are "locked".
Personally, I'd have to think long and hard about buying XPs again, rather than MPs, but it's personal choice and an educated "risk".
Do your research before buying!
Do your research before buying!
p.s. You'll never, never, ever regret going dual..! Want to burn, play CS and rip a film? You got it!