<a target=_new> might work, or if you're talking about a popup window:
<SCRIPT LANGUAGE="Javascript">
<!--
function newwin()
{
window.open("http://www.phpbuilder.com","newwindow","toolbar=1,location=1,directories=0,status=1,menubar=1,scrollbars=1,resizeable=1,width=800,height=600")
}
//-->
</SCRIPT>
then you can call it with javascript:newwin();
or possibly
<body onload="javascript:newwin();"></body>
