you should look at http://www.softwareinreview.com/linux_opti...nsuse_10.3.html, maybe the problem is you don't have the required codecs? is w32codec-all installed. What format is the file you're trying to play? Where did you get the mplayer rpm?

what displays if on the command line you type "mplayer video_file_name" ?

Have you tried other video players such as vlc and kaffeine? remember that you should use the Packman repository because Suse's packages will not play proprietary codecs due to legal reasons.