Audacity will do the job.
Here's a manual for you:
http://www.ehow.com/how_5039268_convert-stereo-mono-mp.html
@Arawn started
London Fixed Gear and Single-Speed is a community of predominantly fixed gear and single-speed cyclists in and around London, UK.
This site is supported almost exclusively by donations. Please consider donating a small amount regularly.
Audacity will do the job.
Here's a manual for you:
http://www.ehow.com/how_5039268_convert-stereo-mono-mp.html