i think you should check out the benchmard of dual system first. for the money, i think single cpu make more sense to me.

here are what i think. if you get a s2640 now with 2 AthlonXP or MP. when the new .13 Athlon come out next year, you MAY NOT be able to use your motherboard. that means you will have to upgrade everything again which i don't think is very good.

second, tyan doesn't offer good overclocking ability. (if you wnat to overclock, of course)

for your money, you can have a decent one cpu system. either a p4 or athlon. again, you should check out benchmark, dual system doesn't offer double performance. for most applications, dual system is even slower than single system!