The SuSE versions were compiled without mp3 support.
Go to the Novel/SuSE forum on this site. There is a sticky on adding a packman repository in "yast2 inst_source".
Uninstall the version you have and install the version from the Packman site. The same goes for xmms, xine, mplayer and audacity.
In YaST2, you can filter by repository. A second filter appears where you can use a search as before.