The same Problem I have encounter with MM while in MMs Plugins Dir exist 2 Plugins that in_port MP3. Try manualy delete/rename some of IN_????? plugins eg. IN_MAD.DLL => IN_MAD.DLL.OFF. Maybe it can help.

"division by zero" error message window pops up when i try to play anything.
occurance started after reinstalling monkey to select yes for the bundled MAD plugin.
I chose no the first time cause i know it's already with Winamp.
removing the programme and directories then reinstalling has not fixed the problem.
gyaresu