You should use mediainfo to double-check the format of the file. http://mediainfo.sourceforge.net
If it’s MPEG, it might be MPEG-2, in which case you’ll need both a splitter and a decoder. I suggest the GPL one.
It might turn out to not be an MPEG at all, in which case report back what mediainfo says, and then we can decide what to do from there.
I have looked for one, but none of them work. I am using MM 6.0 on Windows 7 Starter and it won’t play/let me edit my videos that end in .mpg. Can someone please give me a link or tell me how to get the codec needed to edit my videos?