I should mention that the link provided by FrightfoO only works if you have Windows Media Player 7 or higher. If you have Windows Media Player 6.4 you would need another codec installation package.
The first download on that page is the one posted by fright. If it fails try one of the next two. (I’m not 100% certain, but the third one (the vcm package) may be necessary if the wmv3 is embedded in an avi as opposed to a wmv file)
You can install the WMV9 codecs pack and expect things to work fine, even in WMP 6.4, but if a few things don’t function, you can try the Windows Media Player 6.4 codecs.
I only have the WMV9 codecs installed and things are fine. I use WMP 6.4 (comes with XP - go to run and type - mplayer2 to access it) or WMP8 - both come with WindowsXP :)
you misunderstood me. all three of the codec packages on that page contain the wmv 9 codec. the first one will give you an error message and say you need wmp 7 or higher if you have wmp 6.4, and then setup just exits. That’s why there are alternate packages for people who want the wmv 9 codec without upgrading to wmp 7 or 9.