Ever heard of PartyCloud? It's a great online remixing tool that let's you mash two songs together and change some of their settings, like volume and speed. It has a great button called 'sync' which matches the beats of the two songs together so you don't have to fiddle with them for hours to match them up manually. This is probably the best feature of PartyCloud, because it makes everything so much easier and simpler. From there on, it's all up to you. What songs will you mix? Which sections of the songs? How can you make them go together well? Go on, try it out: http://www.partycloud.fm/

Fair use policy is a great thing for music lovers. It lets artists work off of previous music, thus improving it and their own style as well. It makes sure that artists aren't scared to use other's work as an inspiration. Without fair use policy, artists might even be too scared to write original content, in the off chance that their content would resemble other artist's (and so landing them in jail). So, us listeners really need to be grateful for fair use policy, and how much freedom it gives the artists we love. 
This is a presentation some classmates and I made on a related subject:
https://docs.google.com/a/scollege.cl/presentation/d/1_gvZqcUuWpg8KAuWyixeWN-tN2fApC062W_SeLzfCqk/edit#slide=id.gf949a05a_022