I don’t know how many different ways I can say it – It doesn’t matter if the copyright holder advertises the music as “free”. Profit or lack of it has nothing to do with copyright. Most “free” music on the Internet comes with a license, or terms of use. The license almost always states “for personal use only”. The project you describe is not for personal use. Lack of a license does not mean that the work is in Public Domain; it just means that the copyright owner is sloppy and hasn’t disclosed the license terms.
I am certain that if you look in the website you will probably find something that states the uses allowed. A.K.A, a license.
Any other use requires an explicit license stating how you may use the music. If you don’t have it, you are risking copyright violation. It doesn’t have to be a formal document. It could be as simple as a handwritten note from the copyright owner.
Steve Mann
MannMade Digital Video
http://www.mmdv.com