CO - Importing videos from recording

We began uploading the footage we recorded on Sunday to iMovie HD today (7th November), which as a whole was successful. However, because we used two different cameras, the first one we used recorded in .MPG format rather than the universally accepted .M4A. This means that only half of the footage we shot on Sunday was able to actually be imported into the iMac, but we have begun working on editing the takes we have anyway, and once we find a solution to converting .MPG to .M4A then we can upload that too and simply insert it between takes already on the timeline.