Simple(?) Problem: Disable button after loading a movie? (Flash MX)

OK, i have a navigation with buttons that load external movie clips into a empty movie clip. Yes, very simple.

Im sure some of you experience this problem, if i click on the button to load the swf repeatedly, it will re-load the movie repeatedly (very annoying). I want to disable the button after it has been clicked once, and re-enable it when another button is clicked.

The buttons reside inside a movie clip on the main stage.

The empty movie clip resides on the main stage.

heres the code for one of the buttons:

on (release) {
_root.target_clip.loadMovie(“updates_nav.swf”,“1”);
}

I just want it to load once then disable the button. I tried the button.enabled=false into the brackets but i get no results.

heres my page so far:
http://www.poeticgarble.com/swf/circles.html

(no preloader yet, just updates loaded using a modification of the guestbook found on this site)