[AS2] Preloader: adding filesize from xml

I’m making my first flash web site, and on the Home-site there is 3 images loading from an xml. file.
How can I in the preloader script write that it should find the size of all three images, add them, and use this number to find out how long the loading process has come.

Teh script so far:

this.onEnterFrame = function() {
    filesize = imgLoader1.getBytesTotal();
    loaded = imgLoader1.getBytesLoaded();
    preloader._visible = true;
    if (loaded != filesize) {
        preloader.preload_bar._xscale = 100*loaded/filesize;
    } else {
        preloader._visible = false;

imgLoader1 is one of three empty movieClips that the images are being loaded in to.
But I want to add the filesize of all thre images in some way.