RealAudio support was removed from Windows Media Player because 
only the older version of the Real formats are supported.  You
should use the RealAudio player to play back RealAudio files.

If you really really want to play back RealAudio files using
the Windows Media Player, download and install the DirectX
Media 6.0 Runtime from 
http://www.microsoft.com/windows95/downloads/contents/wuother/directxruntime/default.asp
This includes the Windows Media Player 6.0 with RealAudio 4.0 support.  
You can safely install this over Windows Media Player 6.4, resulting in 
Windows Media Player 6.4 with RealAudio 4.0 support.  
Note that only RealAudio/RealVideo files version 4.0 or lower are supported.


Note that WMP7 can NOT play back RealMedia files with
or without this filter being installed.  Even with this
filter installed, only WMP6 will be able to play back RealMedia files.