A few users at Appleis discussion forum are experiencing a severe problem with the Beta of Boot Camp installed under Tiger, then updating to 10.4.11. The result is that the Mac cannot boot and the only remedy is to extract the user data in FireWire Target Mode, reformat and reinstall the OS.
The thread of the discussion has some helpful suggestions by contributors, but the most important thing is to back up all user data before attempting the 10.4.11 update for those who have a Boot Camp partition. For those who may need to reformat and reinstall, simply booting from a CD doesnit seem to work. A second Mac is helpful along with FireWire Target Disk Mode to extract the user data before starting that process.
One customer who had the problem took his Mac to a local Genius Bar and reported that this may be a known issue. A search of the Apple Knowledge Base, however, did not return any relevant documents.