Follow these steps:
1) Download and install latest version of Goldwave
2) Open ASF-file with Goldwave
3) Save it to WAV or MP3. There are many other formats, too.
Suggested bitrate for new MP3-file is same as the original ASF-file had.
Note, Goldwave uses LAME MP3 Encoder, so Goldwave will ask for "lame_enc.dll" at the first run. If you don't have it already, download it from The LAME Project page.
