Yesterday I loaded recommended patches via Windows Update. Afterward, I could no longer boot into Windows (XP Professional SP2). I'd either get a blue screen of death, or complaints that Windows couldn't boot because various device drivers couldn't be found. After an entire day of troubleshooting (tried reinstalling Windows, etc.) I successfully booted into safe mode, used Add/Remove Programs to remove Parallels Tools, then rebooted and reinstalled Parallels Tools. I seem to be back in the saddle. Your mileage may vary.
