My upgrade to v4.0 WXP and Ubuntu went without a hitch except for loading BackTrack3. It took me a couple hrs but figured out to update the bootloader at the boot menu (w/tab). I had attempted to make updates to the bootlilo.sh script, but obviously r/o even though tried to change the rights to the file. Just add acpi=off to the kernel option of the bootloader and Backtrack 3 will load.
Maybe the Parallels will add code to correct this error in an update.