If you get an "Internal Application Error" while launching Windows Media
Player it is likely not installed correctly.  You will want to re-download a
copy of the player and then install it over your installation.  It can be
downloaded at
http://www.microsoft.com/windows/windowsmedia/9series/gettingstarted/download/do
wnload.asp.

It you are still getting the error after you know the player is installed
properly then it is being caused by something external to Windows Media
Player.

http://support.microsoft.com/default.aspx?scid=kb;en-us;831430 could also
address this issue.

If you have installed any "Codec Packs" at any time they might also cause
this.  It doesn't matter if you have uninstalled it, because the uninstaller
for these third party codec packs only work about 2% of the time. -
http://msmvps.com/chrisl/archive/2004/07/04/9546.aspx

Now, if it's not the player itself and you have not installed any codec
packs at any point then the problem is most likely your video or audio
drivers.  To test this launch mplayer2.exe (Start>>Run>>Type "mplayer2.exe")
and see if you can play video and audio files without issues.

If you run into an issue then it's also likely causing issues with WMP 9
also.  Reinstall both the audio and video drivers to fix that.

If that doesn't do it it's could be the CD-ROM driver doing it.  Please see
http://www.zachd.com/pss/pss.html#usedma for help fixing that.

If none of the above helps you will want to ask real Product Support.  See
http://www.zachd.com/pss/pss.html#psssupport.