I am set to direct a short film in a couple of weeks and a musician will compose music especially for the flick. I have heard that if I want to enter it into festivals and the like, I would need to obtain some sort of release for the musician to sign. My question is, what would this release say, and could I write it up myself and have the musician sign it?

Yep you can write it yourself. Do a search here, or check out the business forum FAQ. There is a link to some release forms there that you should be able to easily modify.

A couple sample release forms in this thread. (http://www.dvinfo.net/conf/showthread.php?s=&threadid=4039)