Stan:
That's wierd! OK, let me try here. First, you can change the file extension to ".mpe", this will associate it with Windows Media Player. If that doesn't work, try selecting the file by left clicking it once. Then hold down the right "Shift" key, then right click it. You should get a window with an "Open With" prompt. Click that and a list of programs will pop up. Scroll through them and select "Windows Media Player". If you don't have a proper decompressor, you will get the message in the video display in the media player.
One last thing-Did you run the set-up executable for the DIVx decompressor you downloaded?
One more last thing! When you get it working, go get that supermotard video. It's a hoot! You'll love it.:)