Just thought you might want to check out Acid Planet and their remix contests. Every day there's at least 3 or 4 remix contests happening. What they do is they take an existing song, seperate the vocals and the instruments, and you can take those in WAV format, mash 'em up however you want, and win cool prizes! This has been going on for years, and is really fun and good practice.
You can also listen to everyone else's remix, and sometimes the grand prize is to have your remix on the song's single album! Pretty cool if you ask me.
(and no, you don't HAVE to use their audio products for your remix)
http://www.acidplanet.com/contests/
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