If you're looking for a program to just slice up some songs and add in a few affects here and there Audiocity is your best option from the programs that I've tried out. I've edited alot with this program and it has never failed me.
Hope I've helped and good luck.
You might want to also check out Noteworthy Composer. It may allow import of MIDI files. You can google "Noteworthy Composer" to get its website. For the price, it certainly does a lot. It's what I use at home for all my composing/editing needs.
Hey yeah, if you really want to get serious about it you can buy Adobe Audition (Which was previously called Cool edit). The radio station where I volunteer at has that program, it is really easy to use. Free Software Downloads and Software Reviews - Download.com has a trial version that you could probably try, but since it is only the trial version it obviously wouldn't have too many features as the actual program.