A while back there was a thread in which performance of different computers was tested with a scene Jim Burton made. The results were that with Poser4 the AthlonXP definitely defeats the P4. That said, Poser5 might behave differently, but I don't really expect it to have special P4 optimizations. If that new render engine leans heavily on FPU (which I expect it will) then AthlonXP will probably again beat the P4. Performance also depends heavily on RAM, so don't forget to take that into consideration when comparing an Athlon and P4 system.