HELP - Preloading a random background

Does anyone know how I can add code to preload a random background?

This is my current random background code-

choice = Math.round(Math.random()*6);
switch (choice) {
case 0 :
location.loadMovie(“bg0.swf”);
break;
case 1 :
location.loadMovie(“bg1.swf”);
break;
case 2 :
location.loadMovie(“bg2.swf”);
break;
case 3 :
location.loadMovie(“bg3.swf”);
break;
case 4 :
location.loadMovie(“bg4.swf”);
break;
case 5 :
location.loadMovie(“bg5.swf”);
break;
case 6 :
location.loadMovie(“bg6.swf”);
break;
}

and this is my preloader code-

bytes_loaded = Math.round(_root.getBytesLoaded());
bytes_total = Math.round(_root.getBytesTotal());
getPercent = bytes_loaded/bytes_total;
_root.loadBar._width = getPercent100;
_root.loadText = Math.round(getPercent
100)+"%";
if (bytes_loaded == bytes_total) {
_root.gotoAndPlay(3);
}

Both were taken from tutorials on Kirupa, but I can’t figure out how to integrate them together. Thanks!

Justin