Well, no, OGM files can be plexed video+sound+subtitles. They can even have multiple audio tracks, angles, chapters, etc. A very versitile format.
If you search a bit on the net, you should be able to find a program to break it into it\'s component parts, and from that you can re-encode. However, if you have all the right codecs (the OGM file plays ok, right?), sound+video, I would think a bit of playing with virtualdub or nandub will work.