Updated Parallels 4.0 Tools (build 4.0.3848) causes 100%CPU with Interrupts

Hi, this has been seen before in earlier versions (2008), but the latest update of Parallels Tools causes the system to be come unusable with 100%cpu usage, most of them Interrupts so I'm guessing a driver/IRQ type problem.

Removing Parallels Tools fixes the problem, however a VM without it is kinda useless

Anyone got any ideas (other than 'Update to Parallels 5')? I can't for the life of me find my older Parallels installer to downgrade right now.. anyone know where to get older released versions from?
Thanks.

System Spec:

MacbookPro 2Ghz Core Duo Rev1
Mac OS 10.4
Guest: Win XP Pro