Flip4Mac, the Microsoft blessed set of QuickTime plug-ins that play most Windows media formats, has been updated to version 2.1 with the major addition being native support for Intel based Macs. To recap, Microsoft has officially discontinued development of Windows Media Player for the Mac and instead endorse Flip4Mac as the sanctioned method to play their media files on Mac OS X. Advantages of Flip4Mac over the old player include: play media embedded in web pages and using QuickTime Player; support for Intel based Macs; it actually works.
You can download the free playback only plug-ins from Microsoft here:
or grab a trial version of the full package that also allows creating WMF files here:
Most people just need the free version.