Finally, someone spends time to work with a Linux server and OS X authentication issue:
OSX has what I would call an undocumented feature of the operating system- the portable home directory. Basically, it keeps a user's home directory sync'd up between a network share and the local pc. If you are not on the network you work on the local home directory. Whenever you login on the network, the mirror agent running on the local pc synchronizes the two directories.