Actually, what you need isn't gstreamer... it is gstreamer xine, or any non SuSE OSS output plugin. The easiest way to get it working in 10.0(note this DOES NOT WORK in 10.1 beta) is to completely uninstall Xine and Amarok(and other media players you installed when installing 10.0 like Totem, Kaffeine, etc) and then do an install either through YAST from the packman or guru repositories of the media players. These media players will be full versions, not distro specific versions. Then you need to install mad, win32codec, and mplayer(and the mplayer-plugin).
You should be set from there.