Dolby AC3 (2000)

I am trying to play a movie using Windows Media player and I can't seem to do

When I load the video in WMP it says "acquiring codec", then "codec
acquired" then when it tries to play there is a little white x inside a red
circle with the title of the movie. When I click on that and can see error
details I go to web help, and the windows site tells me that:

"Windows Media Player Error Message Help
You've encountered error message C00D10D1 while using Windows Media Player.
The following information might help you troubleshoot the issue.
Codec is missing
Windows Media Player cannot play the file (or cannot play either the audio
or video portion of the file) because the Dolby AC3 (2000) codec is not
installed on your computer.
The missing codec might be available to download from the Internet. To
search for the Dolby AC3 (2000) codec, see"

I try going to that site but I can't find the download I need. There are AC3
1.50a, AC3 1.46 stable and I don't know what I need. I thought I needed Dolby
AC3 (2000) but I don't see it there. I don't understand how WMP 10 finds the
codec, and the sound still doesn't play. Why does that happen? What is wrong
with my WMP? Is said acquiring, and then acquired, but no changes are made.

Any help that could be provided would be great.