I installed 3.0 on my MBP (2Gb, 2.16Mhz) because the cam apps were very unstable under 2.5 but when they worked they were fine. I had no performance problems with 2.5. Now 3.0 runs so slowly it is nearly unusable, the monitor shows 30% even when its inactive, if I plug a cam in (built in or real usb) the usage goes up to 70% even with no cam app running. Start msn or quickcam and the usage goes up to 110% even if cam is not being used. Have also installed kasparsky instead of Norton which is the only other change. (All drivers are latest from Logitek) Memory is set to recommended 932kb and guest os is priorised. Can anyone help?
Try setting Enable virtual memory preallocation in Preferences->Memory. It gave me some more performance.
I had a similar problem and used the procedures outlined in the following parallels knowledgebase: http://kb.parallels.com/entry/20/235/ Parallels is now running fine for me.