You don't need cracked warez to make MP3 files for free.

Take a look Here and take your pick.

I use LAME on a Linux command line.

BTW, I fully agree with two points made earlier:
1. Use line input, not mic input on sound card
2. Record to WAV, then convert WAV to MP3. It will take up a fair amount of disk space, but if that's in short short supply you can delete the WAV once you have the MP3.

Anahata