recmp3 is a Windows application which records audio from an external source (tape deck, sound system, etc.) and writes it directly to an .mp3 file using the LAME mp3 encoder.
recmp3 is written for Windows (Win9x/ME/2k/XP)
You may also want to visit the recmp3 Project Page
The readme.txt file provides instructions on running and building recmp3 and provides a revision history
recmp3 makes use of LAME (for the mp3 encoding) and NASM (used to build LAME from its sources). You can use the below links to obtain those products.
LAME mp3 Encoder