For a while VPC2007 worked just fine running Windows Vista. Recently,
however, I find that any active processes suck up tremendous amounts of
CPU time, so that if you're actually doing anything in the guest OS, the
guest CPU time runs at 100% and everything is dreadfully slow.

I can only guess that the change occurred when I upgraded the host
computer's memory (a Dell Optiplex GX280 with a 3GHz CPU and Windows XP)
from 1GB to 3GB.

The computer has XP SP3, and VPC2007 SP1, but this problem started
happening when the computer was still XP SP2 and VPC2007.

Other guest operating systems (Windows XP and 2000) work normally.

I also tried copying a correctly working Vista virtual machine from our
Virtual Server, and as soon as VPC2007 runs it it slows down.

What can I do about this?