n order to reclaim the /home directory, edit the /etc/auto_master file and comment out (or remove) the line with /home in it. You'll need to reboot after this for the change to take effect (or, per nilbus' comment, try running sudo automount -vc). This works with Mac OS X 10.5 (Leopard). Your millage may vary for different versions, but it should be similar.
As noted on that forum post, you should also be aware that Time Machine automatically excludes the /home directory and does not back it up.