FREE Music Mash-up software?

hi. I wanted to make a mashup of songs like DJ Earworm and such (a href="http://www.youtube.com/watch?v=LLA7JMPE_xU)" rel="nofollow"http://www.youtube.com/watch?v=LLA7JMPE_…/a and was wondering what a good, free software would be to use. Not looplabs, please. Also not something that would screw up my computer. Thanks:)