There is an excellent open souce (and therefore free) project called Audacity. I believe it's on sourceforge, but do a google search for it. Alternatively, Nero (my personal favorite burner program) includes a decent audio editor. Their software is totally worth its price, you can find a demo on
www.nero.com. Finally the best, almost professonal grade editor use to be called Cool Edit, and it's now under a different name and is currently owned by Adobe. That's a few hundred dollars. and although I have never seen the Adobe version, the older one was the best.