I'm just beginning to need and use an audio editor. Found this open source application, Audacity, and am very pleased. Bit of a learning curve if you're new to it, like I am, a bit of an adjustment from video editors, but it's free and does basic editing

Get Audacity here:
http://audacity.sourceforge.net/

If you want to save to mp3, you'll need the free LAME library; it's available for a variety of platforms.

The download page is kind of confusing. Below is a direct link to the Widows exe as of 2011-06-25; you'll want to check the main page if you are reading this much later than 2011-06-25, since a more recent version may be available.

Lame_v3.98.3_for_Audacity_on_Windows.exe
http://lame.buanzo.com.ar/Lame_v3.98.3_for_Audacity_on_Windows.exe

Main LAME for Audacity download page
http://lame.buanzo.com.ar/