You'll need to download and compile the vorbis player/encoder tools for everyone from vorbis.com. Its kind of tricky; you'll need to install libao2, libogg and libvorbis libraries using fink, then compile with the following:
./configure --with-ogg=/sw --with-ao=/sw --without-flac
I didn't bother to compile with flac support, because I use flac to do that. You might get some errors during the configuration, and they are pretty good about what's causing the problem. If you're missing any libraries, check to see if fink has (or can) install them. You'll also need to install LAME with fink. It was simple.
Finally, here's the shell script that you can run in a directory full of .ogg files when you're ready for bed. Feel free to change any of the options in the lame converter, and see ChrisR's post for information about IDv3 tags with command line tools if you're interested.
#! /bin/sh
# Andy Freed - 2004
# this uses fink installed flac to convert
# .ogg vorbis audio to .mp3 files with
# the fink installed LAME encoder.
# modified from flac script by ChrisR on MacOSXHints.com
for file in *.ogg
do
ogg123 -d raw -f - "$file" |
lame -h -m s -b 192 - "$(basename "$file" .ogg).mp3"
done
[robg adds: I haven't tested this one ... and remember to make the script executable (chmod 755 script_name).]

