When I was in college we used to do it like this
on (release) {gotoAndPlay(2);
}
with the number in the brackets being whatever frame your movieclip starts on.
To stop it repeating just make a new layer and put
stop();
on the first frame.
That should work but I might be a bit rusty as I haven't touched flash in over a year
edit: Just seen that Andrew has just posted practically the same thing so it looks like I remembered rightly for a change