Who says you can't play mp3s on a Mac old enough to be in a museum? These guys sure don't:

The biggest reason to use MpegDec is that it can play MP3 files in realtime on almost any Mac. Even 'older' Macs with 68K processors are now able to play MP3's.

MpegDec also offers quite a few features at an incredible price - free. And the feature list is growing rapidly. Whether you have a new PowerMac or an old Quadra, you owe it to yourself to try MpegDec on your system.