Please help a newb

Hey guys, I am having a problem in flash ,and I need help. Here is what I got I have a flash site. It is a site map. And on the click of one of my buttons I want it to replace the background image with a new background image and then when you click again I want the old image to come back. like a loop of just the 2. here
is the code I have to the background which is a mc

onClipEvent (load) {
var nowloaded = “test”;
trace(nowloaded)
}

AND HERE IS THE SCRIPT FOR THE BUTTON

on (release) {
if (nowloaded == test) {
empty_bg.loadMovie(“bg.swf”, 1);
(nowloaded == test2);
} else if (nowloaded != test2) {
empty_bg.unloadMovie(“bg.swf”, 1);
empty_bg.loadMovie(“rbg.swf”, 1);

nowloaded = “test2”;
}
}

I have Just started to learn flash so please speak in newbish terms Anyones help would be appreciated greatly