Sound Forge Rocks!

If you are going to use your voice (or your voice as a robot) to explain your "how to" movie I recommend Sound Forge. My co-worker turned me on to it and it is very robust and easy to use. I used 100% voulme and medium room reverb and it sounds pretty good! Here is one of many sites that you can download a trial version. - no MP3 support though :(

http://www.hitsquad.com/smm/programs/SoundForgeXP/