Hi Saeed,
If you're trying to import a .dat file which has video into MM2 chang ethe
"Files of type" dropdown in the Movie Maker import dialog to 'All Files
*.*', then you'll be able to select the .dat file to import into MM.
Be aware that MM2 will only support files for which the correct codecs are
installed on your machine (and those codecs work within MM).
-Gareth