Rescale movieclip based on browser size

hi

im trying to resize/scale a movieclip based on the browser window.
i sort of got it working. but my prob is that i dont want it to scale beyond the browser size when u just stretch the width or height.check it out

http://www.numero97.com/loader.html

if u stretch just the width of the browser the image enlarges which i dont wont it to. hope i am making some sense.

heres the code/formula used in a onResize

var mywidth:Number = 955;
var myheight:Number = 575;

Enlarge = (Math.round(Stage.height/myheight100)+Math.round(Stage.width/mywidth100))/2;

_level0.container_mc.main_photo_mc._xscale = Enlarge;
_level0.container_mc.main_photo_mc._yscale = Enlarge;

can anyone help me on this. i think its just to with the formula used for Enlarge.

cheers

Andy