In one of my recent projects, I had the requirement to open a browser window from within Flex on click of a button. Thats when I came across this Externalinterface call. Here is how I did it.

private function openWindow():void
{
ExternalInterface.call(“w_ = function () { window.win = window
.open(‘http://yahoo.com’,'TestPage’,'width=700,height=500′); }”);
}
Dont forget to do this though :-

import flash.external.ExternalInterface;
Might be useful to some of you trying to achieve the same in your project.