VLC can play them fine but I havn't yet found a program for Mac that can repackage the streams (convert ogm to avi), However...
...I do know of one that i found for Windows, It's called "Virtual Dub" and it can split an ogm file into its independant streams, or fully convert to a new format. Its a free download ,just google "Virtual Dub Windows Download" and you should find it.
However if anyone knows any good mac aps for this id like to know 2.