"So full it won't boot up..." sounds pretty silly to me, but, if that is indeed the case I would simply recommend booting from a LiveCD or jump drive, saving what you have on the disk to a networked drive, and doing a reinstall.
I haven't ever ran into a situation where the OS overwrote its own boot sector unless I specifically told it to do so (no matter how 'full' it got).
Maybe, if he is savvy enough, he can load a microlinux (?) distro onto a jumpdrive with Samba installed on it to extract his needed data. Nonetheless, backups should have been performed as well, now maybe he will have the needed impetus. |