1.>If you got the files from video cd's then rename the file and convert it into .mpeg (simply change the .dat to .mpeg)
2.>Yes, to add .dat files, you'd need to do that.
I'd recommend the renaming into mpeg or avi, as most people won't search for .dat for movies, more often, it's .avi or .mpeg
Always rip songs into .mp3 using cdex and not .mwa using windows media player, an Wmp encodes information about your computer, so that the file can be traced back to you....
Cheers