How to change GDM3 themes and how to install GNOME sound themes?

I started using Linux as an Ubuntu user and when I switched to OpenSUSE I used KDE for a while but now I’m using GNOME 3.2. I’d really like to modify my GDM theme (and change the login background) and I didn’t quite like the muteness of GNOME on Opensuse so I thought about installing the GNOME Sound Theme manager, however It doesn’t seem to run on OpenSUSE. Is there a workaround for this? Or is it impossible to modify GDM3 and the sound themes? If it is possible, what steps should I follow?