Safari and MIME type “application/x-mplayer2”

When trying to listen to web pages conatining mp3 audio files (prior to purchasing them) , Safari comes up with a message saying that MIME type “application/x-mplayer2” is not installed and only downloads the html file and not the mp3 file. When we check on our installed plug-ins in Safari, MIME type “application/x-mplayer2” has been installed.

How do we fix this? We are using Safari Version 2.0.2 (416.12) OSX 10.4.3. It works on one of our older machines running Safari Version 1.3.1 (v312.3.3) OSX 10.3.9

Regards,
Peter