Center a Movie Clip on 100% Stage

[phatbyte]

Hello Community

How i can get a Movieclip centered on a 100% Stage?
Stage.align = T; doesnt work

and this also not works
mc._x = (Stage.width/2)-(mc._width/2);
mc._y = (Stage.height/2)-(mc._height/2);

Thanks in Advance
Oliver