There is a bit more to it than that. The main function is window.open which is a built in function of javascript. There is a script somewhere in that page called windowOpener.
function windowOpener(url, name, w, h) {
eval("msgWindow=window.open(url,name,'width=" + w + ",height=" + h + "');msgWindow.focus();");
}
I wouldn't advise on using that script. It uses a very old method called eval. It is rarely ever needed. Try this
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<title>Untitled Document</title>
<script type="text/javascript">
function openWin(url,name,wid,hgt){
sw=(screen.width-wid)/2;
sh=(screen.height-hgt)/2;
newwin=window.open(url,name,'width='+wid+',height='+hgt+',top='+sh+',left='+sw+',scrollbars=0,menuba rs=0,toolbars=0,directories=0,location=0,address=0');
newwin.focus();
}
</script>
</head>
<body>
<a href="http://www.yahoo.com" target="_blank" onclick="openWin(this.href,'somename','400','400');return false">Some Page</a>
<a href="http://www.htmlforums.com" target="_blank" onclick="openWin(this.href,'somename','400','400');return false">Some Page</a>
</body>
</html>
This way if the user has javascript disabled the page will still open but in a full sized window instead.