I use a bit of software called Goldwave to do all my sound editing. It's a very powerful sound editor, along the lines of SoundForge (a prefessional sound editing software used for making hollywood movies) but it's a bit simpler and more user friendly. The best part is it's shareware. You can use the fully functional trial version forever, but it will only let you perform so many actions before you have to restart the program. This software is something you can use to rip music from DVD's, music CD's, or off of your computer or your television, it can record and play back in virtually every sound format known to civilized man, and it has hundreds of sound editing features that you can use with one click buttons that you can configure to your liking. I used it to make the sounds mod I just released for SFC3 on the TNZ News webpage. I took some sounds from the Nemesis DVD, some from the internet, some from television, some from other games I was playing while recording at CD quality level, and some that I recorded with a microphone and distorted with Goldwave's awesome features. you can mix sounds together, seperate lyrics from music, and do a TON of other things. And if you want the full registered version, it costs just $40. This is probly the best $40 I have spent on any non-game software on my hard drives. I can't imagine being without it. It's the "Photoshop" or "3D Studio Max" of sound editing. I've used it more than any other software that I can think of. And since it's useful beyond just game mods, the $40 is easy to justify. Try the trial version, you will be amazed by what you get for $40.
http://www.goldwave.com/