Need help with background

hey guys hope you can help, i have just started out in as3 i am buliding a full flash site, i have a png image for my background , and polaroid images flying in and resting on top using tweening. i need to have the png background image resize to fit the whole browser window at different reolutions and the polaroid content to stay centred, i think i will need to export the polaroid content without background have a new fla open with just the background and load polaroid swf externally through the use of use of ui loader to load , i need a script to be able to do this , i have looked everywere (4 hours in total to find one, or a video tutorial showing how, ive found a as2 that works well but cant use ui loader as its as3, so im really stuck ,any help would be appreciated thanks guys.