Open URL in a target div

I need some actionscript help.

I have a DIV with an iframe inserted into it on my webpage. I am trying to get my flash button to open a URL within that iframe without refreshing the entire page. Is there a way to accomplish this? Here are some details about my HTML and Actionscript:

HTML:
<div id="graynav"><iframe src="gravnav.html" name="secondarylinks" width"175" height"349" frameborder="0" scrolling=no"></div>

Actionscript:
button1.onRelease = firstlink;

function firstlink() {
getURL("graynav.html", "secondarylinks")
}

Do I need to specify the target in a different way? Any help would be appreciated.

Thanks.