Hey guys, does anyone know of anything that will let me play MPEG-4 videos on my computer? I am running openSUSE 11.1. Thank you!

mplayer generally plays anything I throw at it, including mp4's.

Have a look at Vlc.

http://www.videolan.org/

It should be available from your package manager.

Better than that...

Vlc has an installer for openSUSE 11.1.

http://www.videolan.org/vlc/download-suse.html

If you use this installer, you can have mplayer, amarok with xine, mp3 support K3b, etc

http://opensuse-community.org/Restricted_Formats/11.1

You can have many player, I do.

You could just add the repositories for VideoLan and Pacman for all the restricted codecs.
YAST > Software repositories > Add > Specified url > then paste one url (below) at a time then repeat for the second url.
Then you will normal functionality in YAST and for zypper.
It may be noteworthy to use the Pacman versions for everything that is shared with VideoLan since it works with more applications which exist in Pacman. I set the priority for Pacman to 40 and VideoLan to 50 so updates work without going to each updated package to be sure which version is coming down from what vendor. You may also want to change the update repository to 40 as well so system updates do not over write the versions with restricted codecs/features like K3b (MP3 support), KTorrent (DHT features) and others.
You also can select Community Repositories that will download a list which you can just select and apply. If you use community repositories, be aware that the repositories are then just listed as numbers in Software management. So I usually add them manually to obtain names in Software management for each repository (much easier to figure out who is who for example > Repository #1 is vague but Pacman Repository is specific)