Control Button Properties from JS on HTML Page

I'm loading content pages into an iFrame. The Flash menu movie is on the parent page. I'm trying to control the _visibility of buttons on the menu via onLoad and onUnload functions on the content page. For instance, when the Home Page is displayed in the iFrame, I want to change the Home Page button on the menu to a button instance named "home_btn_active." But I can't seem to be able to get the script to find the button and change it's properties. How do I point to the button from the content page and change its visibility? Anybody have a clue? Been stumped on this for more than a day. Thanks.