Good luck building a system like that with any kind of a budget in mind.
Also, most of today's OSs really don't support multiple processors that well, that is unless of course you are running multiple resource demanding programs. Then assign one program to a proc and another program to another proc.
Just wait until 1st half 2005. The Athlon 64 FX with be Dual Core. That means that a stock Athlon 64 FX will basically be two procs. Get a 4x mobo, and you will have the processing power of 8 procs

Not to mention, 64 bit.