I am used to KDE, but I like Gnome and am currently using it...but. I just got a new login gdm theme, how do I change it? I have it copied to the directory it should be in, but where do I go to choose it as default?

Launch GDM setup. You can find it from the Gnome system menu, it's called something like "login manager setup" or something. Or you could launch it from the terminal, if you're unsure about the name, type gdm in the terminal and press TAB twice after which bash should give you a list of what's available -- pick up the command that is most probably gdm's setup/configuration program. When it launches (note: you need to run it as root), it's a nice GTK window where you can pick your theme (if it's copied to the correct directory) from a list, among the other options.

Another way to find out the command using terminal:
provided that you have (s)locate installed and it's database was rebuilt after GDM was installed, meaning that it's rebuilt after the installation. If not, run updatedb as root.

Thanks. I will try that out soon. I am currently at school being forced to use a Win98 computer-and its very slow. I will have to try it out when I get home.