P5 is slower then 4...no doubt about it. Let's start here :) Make sure your temp files are all cleaned up. defrag the hard drive...you should do this prior to install, but now if you haven't done it. I have a 1.53g AMD...P5 is slow, but not as unbearable as you state...

Humankind has not woven the web of life. We are but one thread within it.
Whatever we do to the web, we do to ourselves. All things are bound together.
All things connect......Chief Seattle, 1854