hey, problem is my debian system boots fine, and this problem occurs with all kernels i have installed, 2.4.27, 2.6.8, and 2.6.12. i get to the GDM login screen, and when i type my username and password in (this still happens as root too, and if i choose a different session), it gives me an error saying it can't log me in because it can't write to my authorization file because either my home folder is full or there's something wrong with the permissions. i fixed it once by booting into slax and making some space in my home folder, but i tried that again to no avail, and now i can't login. any ideas?

Maybe you could try deleting the $HOME/.gnome2/session file(s), although I'm not sure why that would stop root from logging in.

root, of course, can not log in from the gdm login screen unless you've edited the security settings.