i did the first one by editing the movie clip if you edit it in a new page you will see a small cross that is the reference point, so your code worked only the MC was off center...
here is a way to do it with action script appologies for the crappy buttons
ok its 4am here and i need sleep... when you say centered on the stage do u mean u want them to stop and not to keep moving? or you want them to click into place? heres another...