If you get musicians to cover a song, in whole or in part, you will need a mechanical license - (a sample is a master use license)

The est. fee is 8.1 cents per song per UNIT UP TO five minutes in length and you obtain this license from http://www.harryfox.com

You pay the license in advance based on units you press (intended sales) and must pay before each new run (so lets say you make 500 to start, you pay based on 500. Before you sell any of the second pressing you must pay again.)

Making sense? Let me know if this is still unclear