Not all mpgs are mpgs.. sounds weird but its true. There are two main types of mpeg, mpeg1 (the really old format that is about the most compatible format you can find, VCDs use this), and mpeg2 (which is what dvds use, SVCDs use this).
Best thing to do is find a software DVD player and try opening the file through that.
To reencode it, go here
www.doom9.org they have many very good guides :)