First Register a username with password, then download the WinAmp Plug-in here. After you sign up, you should get an email stating the url of where your Audio-Tracker image is being served.
For Example:
Your image is being served at http://at.candt.net/scripts/song.php/username
So all you will need to do is put this code in your signature:
http://at.candt.net/scripts/song.php/username%5B/img]
just make sure to replace the url with the one supplied in your email from Audio-Tracker.
If you want to change the color of the text or background simply add the desired hexidecimal color after your url like so:
http://at.candt.net/scripts/song.php/username/990000/ffffff
where 99000 is the text color (Red in this case) and ffffff is the background color (white in this case)