Dynamically loading images

i have done a bit of actionscripting involving loading .jpgs from an xml list based on a drop down menu, but i was trying to figure out if there was any way to load either gifs with transparent backgrounds, or similar, different shaped image files from an external source.

basically, im trying to load an image of a doorknob and an image of a door and have a user drag the doorknob onto the door and see what it looks like

any help would be greatly appreciated. thanks!