I tried playing avi files on my computers (at home (windows 2000) and
at work (windows XP)), but I keep getting the same problem.  When I
click on the file, windows media player opens.  It has a message in it
"attempting codec download", which is followed by the message "Unable
to download an appropriate decompressor. (Error=80040200)".  How can I
view this file in windows media player?

Download and install ffdshow codecs

http://sourceforge.net/project/showfiles.php?group_id=53761

This may sound like a stupid thing to say but was the computer
connected to the internet when you tried to play the files?

Also what version of Windows Media Player are you using. You obviously
used Windows Media Player 9 or below on the Windows 2000 computer but
did you try Windows Media Player 10 on the Xp computer?

Also have these files ever worked in the past? If not the may be corrupt.

You could try uninstalling windows media player from the computer and
reinstalling it again from the Microsoft website.

Your best bet though is to try to view the files through a different
application such as RealPlayer. This way you'll know whether its the
files that are the problem or Windows Media Player.

There is a codec pack that plays pretty much everything works for me:

http://www.codecguide.com/download_kl.htm

To find out exactly which codec is required by Windows Media player,
just download G-Spot (freeware) and point it to the AVI. It will give
you the name of the video/audio codec(s) you need, then you can just
google for them. You can download G-Spot at
http://www.free-codecs.com/download/GSpot.htm

Thank you for everybody's suggestions!!

> This may sound like a stupid thing to say but was the computer
connected to the internet when you tried to play the files?

I can completely see myself making this mistake, however this time the
pc Was connected to the internet.

> Also what version of Windows Media Player are you using. You obviously
used Windows Media Player 9 or below on the Windows 2000 computer but
did you try Windows Media Player 10 on the Xp computer?

Thanks - I will try it!

> Also have these files ever worked in the past? If not the may be corrupt.

I am getting this problem with all avi files.

> Your best bet though is to try to view the files through a different
application such as RealPlayer. This way you'll know whether its the
files that are the problem or Windows Media Player.

I didn't realize one could view these files in Real Player or Quick time!

Once again - thanks a lot - I will make sure to post here again
describing the solution that worked.

I tried
http://www.codecguide.com/download_kl.htm but it didn't work.  

http://www.free-codecs.com/download/GSpot.htm worked perfectly!!

johnmanley-ga please post your comment as an answer, so that I could pay 
for your advice.

Thank you!