Home directory on /mnt/zip

[Geoc]

I'm trying to set up a laptop with RH 8 where most non-root users will have their home directory in /mnt/zip, and EXTREMELY limited access to the rest of the system, and /etc/profile will be set up such that logins will be unsuccessful unless a Zip disk is in the drive.

This is all mostly straigthtforward, except that login attempts as any user with /mnt/zip as his/her home directory fails, and here are the contents of the .xsession_errors file:

Could not open lock directory for xml:readonly:/etc/gconf/gconf.xml.mandatory to remove locks: No such file or directory
Could not open lock directory for xml:readonly:/etc/gconf/gconf.xml.defaults to remove locks: No such file or directory
Failed to unlink lock file /mnt/zip/.gconfd/lock/ior: No such file or directory
gconf-sanity-check-2 did not pass, logging back out

And, here's the pertinent line from /etc/fstab:

/dev/hdc4 /mnt/zip vfat rw,user,exec,nosuid,auto,mode=0777 0 2

Also, as a possibly related issue, root cannot open the zip drive for formatting -- the resultant error dialog reads:

Unable to open the device /dev/hdc4, formatting cannot continue.

Even with umask set (temporarily) to 000

So, what am I doing wrong?