Virtual PC for mac on intel will NEVER run at normal speed. If that were the case then Virtual PC for Windows would be just as fast as windows and its not, its a dog.
Or change the process priority settings of your virtualpc instance to 'normal' while in and out of focus if you have to stick to virtual PC.
But of course, any emulated environment will run slower than a native one. After all, the processor is directly used, but the peripherials still need to be emulated...
I'll move to the MBP, or its hopefully, newly redesigned equivilent, in around a year I think. There'll be better chips, cards etc, as there always is. I might even wait until Leopard is released so I don't have to pay for it separately. (I know, I'm a tightass)
Though I desire the latest and greatest, realistically, my PB should last me at least another 2 or so years, but I know I won't be able to hold out that long.