use a javascript function that the flash triggers, same way you'd launch a sized pop-up etc.
like this (did a quick search cut and paste - needs modifying - but you get the idea) :
in the html
PHP Code:
<script language="JavaScript">
function openNewWindow(URLtoOpen, windowName, windowFeatures) {
newWindow=window.open(URLtoOpen, windowName, windowFeatures); }
</script>
in the last frame:
getURL ("javascript
:openNewWindow
('yourpage.html','thewin','height=300,width=400,to olbar=no,scrollbars=yes')");