To clarify: I currently have this script on the button in the Flash movie:

on (press) {
getURL("javascript:NewWindow=window.open('comp_pop-up.html','newWin','width=520,height=808,left=20,to p=20,\toolbar=No,location=no,scrollbars=yes,status =no,resizable=yes,fullscreen=no'); NewWindow.focus();\r void(0);");
}

Only thing wrong with this is that it doesn't x and y centre the pop-up window.