Hello Jason,
Windows Media Player can play some AVI files and not others because they can be encoded with different codecs (WMV8, WMV9 etc.). If you install the K-Lite Codec Pack then you'll be able to play 99.9% of video formats in Windows Media Player.
K-Lite Codec Pack
1. Go to:
Free-Codecs.com :: Download K-Lite Mega Codec Pack 7.2.0 : The K-Lite Mega Codec Pack includes the K-Lite Codec Pack Full, QuickTime Alternative, Real Alternative support and Monkey's Audio DirectShow decoder.
2. Scroll down to find the link that will "Download [ K-Lite Mega Codec Pack X.X.X ]" where the X.X.X will be the version number
***If the link doesn't work then choose one of the links with "MIRROR" written next to it***
3. Click on it and save the file to your documents
4. When it finishes downloading, find the file and run it
Now we have to install the program:
1. Click Next
2. Check "Advanced Install" and click Next
3. Click Next
4. On the drop down menu, select "Profile 8: Lots of stuff (without player)" and click Next
5. Click Next
6. Click Next
7. Check the "Windows Media Player" box and click Next
8. Check both of the boxes:
-"Video file extensions:"
-"Audio file extensions:"
and click Next
9. Click "Select All" and click Next
10. Click Next
11. Click Install
Tom