I frustratingly found that even after installing a brand new copy of Windows Media Player (WMP), it simply would crash on startup under Tiger.
The fix was really, really simple: Just throw away the files in your ~/Library/Preferences folder that begin with "Windows Media." If there are WMP related files in ~/Library -> Preferences -> Microsoft, then trash them, too.
WMP should work on relaunch...
Mac OS X Hints
http://hints.macworld.com/article.php?story=20051030193221747