g-san writes "Some Mac users are having problems with the latest 10.4.11 update, yours truly included. The problem seems to be caused by the presence of a Boot Camp partition and renders the Mac unable to reboot after the update fails. Note the Geniuses at the Apple stores are recommending a full disk wipe; but data can be recovered via Firewire."
MacNN has a note up that if you fall victim to this "known issue" and need to reformat the disk, you can't reinstall Boot Camp
because it is no longer available to OS X 10.4 Tiger users.