Yeh just thought I'd give this site a solution (rather than spamming it with my questions all the time!). It's not much, and very simple, lamer-easy-ness, but still worth it; until the end of computers.
gdm came back to me saying "gdm user doesnt exsist" etc etc.
1) Don't edit gdm.conf.. Or to be exactly like me..
$mv gdm.conf <where_ever_u_want>/old_gdm.conf
$cp factory-gdm.conf gdm.conf
.. But I think that's the same~!?!!!
2) Add gdm group
('I' to edit, then <esc> and ':x' to save and exit)
gdm::<new&different_group_number>:<users, e.g. gdm, root etc.>
3) Add gdm user
4) Change user and group ownership of '/var/lib/gdm'
$chown gdm /var/lib/gdm
$chgrp gdm /var/lib/gdm
Then run gdm ($gdm). Should work like a treat!