Most of the stickies in this forum are seriously dated for the basic issues; anyhow, here's a thread I recommend replacing them with, which just refers to the instructions from the community website:

This howto is version-agnostic (presuming 10.0+), as the tutorials are demarcated into version sections. Firstly, there is adding the relevant Package Sources:
http://opensuse-community.org/Package_Sources

This will add:

• Online OSS/Non-OSS Source
• Packman
• Guru

Once your package sources are enabled, you can then simply install the necessary packages you will require for enabling certain Restricted Formats:
http://opensuse-community.org/Restricted_Formats

This includes:

• MP3 Playback
• Playing Encrypted DVDs
• Playing DiVX/xvid videos, and
• Windows Codecs

For other questions, you may want to see the general FAQ on the openSUSE Community site.

Also many individual repositories for the latest software. Probably not recommended (or supported) in general, but it's how I upgraded from the default xorg 7.1 to xorg 7.2 to fix my intel video compatibility.

http://software.opensuse.org/download/

The Build Service has plenty of repositories, but note that you also don't have to go looking through them manually. We've got a Package Search set up now at:
http://packages.opensuse-community.org

For upgrading popular packages, there's always instructions around anyway. For example:
* Installing and upgrading Beryl, see http://opensuse.org/Beryl
* Upgrading KDE: http://opensuse.org/KDE/Upgrade
* Testing KDE4 packages: http://opensuse.org/KDE4 (though it might be worth trying out KDE Four Live instead)

...but as mentioned, a lot of this is covered in the FAQ.