I have a 2.0Ghz Pentium 4 with 1Gb or ram & at times Poser5 is slower than poser4, I have ripped the content paradise out though which does give a small speed improvement, check out http://www.poserpros.com/forums/viewtopic.php?t=16569 if you haven't already :)

Windows 7 64Bit
Poser Pro 2010 SR1