So I have a friend who really likes this girl... thing is, in fact, she isn't really into him, and she has expressed interest in me...

Ummm... what do I do so that I don't hurt my homeboy, and get this ball rollin'?

Well if you knew your friend liked the girl why are you considering going out with her? If you plan on doing this anyway just try and break it to him as sensitively as you can. Say something along the lines of, "Hey you know that girl your into? Well she was wondering if we could see a movie together, and I just wanted to let you know I dont have any intentions of hookin up with her really." And if things start happening with the girl just tell him he didnt take the initiative to hook up with her in the first place.. HOWEVER whatever you do dont go on a date with this girl and not tell your friend anything because that would hurt him more I would know.