.mod files are mpeg2 video and ac3 audio (dolby) movie maker may need the codecs to play these, it is getting a bit old, try changing the .mod bit to .mpg
Edit: Just looked here:
http://support.microsoft.com/kb/308464/en-us
and this:
http://www.microsoft.com/windowsxp/u...eofilters.mspx
so recon you will have to convert (re-encode) to use movie maker (may work in the vista version?) or use another editor.