I am running 32 bit Vista in Parallels Desktop 4 on my MacBook (2 GB, 320 GB, Mac OS X 10.5.7, Parallels 4.0.3844). I have two problems with the setup. Whenever the MacBook sleeps and wakes up again, the guest OS in the windows (i.e. Vista) freezes and needs a hard reboot to come back again. And whenever Parallels is running the MacBook's fan comes on and remains on all the time until Parallels is shut down again.