CLI method .. For command line junkies.
"cd" to the directory containing your .ogg files:
cd /path/to/directory/containing/ogg/files
Run this command to have ffmpeg batch convert all the .ogg files to mp3:
for name in *.ogg; do ffmpeg -i "$name" -ab 128k -map_meta_data 0:0,s0 "${name/.ogg/.mp3}"; done;
That will convert ALL the .ogg files to (128k bitrate) .mp3 .. it will automatically change the file extension .. and it will keep all the ID tag metadata.
If you want to use a different bitrate .. just change the
128k to your chosen bitrate.
GUI method .. for everyone else

Simple, install the
soundconverter package .. or if you're using KDE,
soundkonverterNow use it to convert your files.