I'm not the best on actionscript, but i think i know the answer to your question..let's see...
First of all create a layer named "actions" on your main time line AND in your Movie Clip, so you can add your actions ON THOSE LAYER. Then give your mc an instance name, something like "Myclip", or anything you want.
on the FIRST FRAME OF YOUR MOVIE CLIP add this action: "stop ();"
on the LAST FRAME OF YOUR MOVIE CLIP, if you want it to keep looping, add this action: "gotoAndPlay (2);", if you want it to stop and don't loop, just add "stop ();" to the last frame of your MC.
Now, on the frame of your main timeline where you want the movie clip to start playing, add a keyframe to that frame on your actions layer first, and add this action: "_root.Myclip.gotoAndPlay (2);".
If i'm not wrong, that should solve your problem. I might be wrong due to the fact that i barely know some newbie actionscripting, but i did my best to help you, try it and tell me if worked. ;D <hopes>