center movieclip

ok, i'm making a flash gallery (original eh :))
so i have a scroll pane that contains my images, each image is a button that launches popup movie, inside that movie is another movie that loads my image. i'm trying to center the image to the stage but it's taking its stage values as the movie. if that makes sense the line in bold is the one causing the problem. i can provide full fla source if anyone can help


here's my full actionscript

i'm using cs3 and as2

function DisplayInfo() {
infobox_mc._visible = true;
infobox_mc.content_txt.text = this.imageDescription_text;
loadMovie("portfolioImages/"+this.imageDescription_text, infobox_mc.mainImage);
infobox_mc._x = Stage.width/2;
infobox_mc._y = Stage.height/2;
infobox_mc.mainImage._y = -infobox_mc.mainImage._y/2;
infobox_mc.mainImage._x= -infobox_mc.mainImage._x/2;
import mx.transitions.Tween;
import mx.transitions.easing.*;
new Tween(scrollPane, "_alpha", Strong.easeIn, 100, 20, 0.5, true);
}