1) Download libid3tag and libmad from freshrpms.net
or repo of choice.
2) Download the mad plugin for gstreamer from gstreamer.net or repo of choice.
3) Install all three with rpm -Uvh on the command line or using a GUI tool like synaptic
4) Run gst-register to update gstreamer.
5) Optionally run gst-inspect [name of plug-in] to make sure the plug-in was installed correctly.
6) Run rhythmbox and enjoy your mp3s.
The process is very similar for flac support in rhythmbox and lame/flac support in sound-juicer. However, the version of sound-juicer that shipped with Fedora Core 1 has a bug in its extraction loop that causes it to crash after extracting one song with any encoder but oggencode. So, you must update you version of sound-juicer to use lame easily. I'll post RPMs for this in a few days. Thanks.