I think a single pentium 4 would smoke two coppermines. No question any dual core AMD or Intel chip would definitely smoke a couple coppermines, even the nice ones. (1.4 GHz or more) Sorry to disappoint you but your not going to see much performance out of a system from 2001 Even with SMP.
Maybe a higher clocked P4 would. The big performance killer would be the choked FSB on a P3. The quad pumped bus on a P4/C2D, or HT on an X2, would make that dual P3 say nighty-night. Without question there is no way such a setup would be able to meet SMP folding deadlines.
But you have to admit, it would be fun to build if it were really cheap to do so.