Audacity is a good tool for recording voice and saving it in mp3 format.
I recommend to download and use at least Audacity 1.3 (beta) because it provides auto recovery support in case your recording crashes for any reason. (Happened to me 2-3 times when recording in 1.2 version.)
For mp3 support, you need to download LAME MP3 encoder as well from the same download page.
Audacity can also be used for cutting and joining mp3 files.
Screenhosts are available.