Cool alignment

Is anyone good at aligning movieclips to certain points of a stage that runs at full screen? I was wondering how to align an object to the top left corner of the stage which is 800x 600. The tricky bit is that although my stage is 800x600 it runs at full screen but I still want to align my movieclip to the top left of the 800x600 movieclip which is centered… not the top left of the expanded screen. Can anyone help?