To add to Brad's comment,
If you don't want to contact the publishers directly, you can just pay the statutory mechanical royalty through the Harry Fox agency (http://www.nmpa.org/hfa.html). It's currently 7.55 cents per song or 1.45 cents per minute if the song is over 5 minutes.
You would still need to find out exactly who the publisher is from the links that Brad provided. If you want to try to negotiate a lower rate, contacting the publisher is way to go.
One note about the original material. If it's original material, you should also file form SR once you have a finished recording (i.e. mastered copy, printed artwork, etc.). If you're already there and you are the only author of the music, then you can file form SR and it will cover the lyrics, music and the sound recording.
[This message has been edited by Rev E (edited 04-03-2000).]