You need to unistall and then re-install from CD. Luckily you shouldn't lose your virtual machines, but I still recommend backing them up before the uninstall. I've been having a lot of issues with Windows XP on my Fusion and I finally found a workaround to prevent the virtual machine going to 100% CPU all the time. All I had to do was stop using Mirrored Folders ;-) Too bad this is one of the most important features imho and disabling Mirrored Folders makes using the virtual machine a bit difficult.