Probá:
Código PHP:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" />
<title>Documento sin título</title>
<script>
function getWindowData(){
var widthViewport,heightViewport,xScroll,yScroll,widthTotal,heightTotal;
if (typeof window.innerWidth != 'undefined'){
widthViewport= window.innerWidth-17;
heightViewport= window.innerHeight-17;
}else if(typeof document.documentElement != 'undefined' && typeof document.documentElement.clientWidth !='undefined' && document.documentElement.clientWidth != 0){
widthViewport=document.documentElement.clientWidth;
heightViewport=document.documentElement.clientHeight;
}else{
widthViewport= document.getElementsByTagName('body')[0].clientWidth;
heightViewport=document.getElementsByTagName('body')[0].clientHeight;
}
xScroll=self.pageXOffset || (document.documentElement.scrollLeft+document.body.scrollLeft);
yScroll=self.pageYOffset || (document.documentElement.scrollTop+document.body.scrollTop);
widthTotal=Math.max(document.documentElement.scrollWidth,document.body.scrollWidth,widthViewport);
heightTotal=Math.max(document.documentElement.scrollHeight,document.body.scrollHeight,heightViewport);
return [widthViewport,heightViewport,xScroll,yScroll,widthTotal,heightTotal];
}
function abrir(W,H){
var pagina=getWindowData();
document.getElementById('capa').style.width=W+'px';
document.getElementById('capa').style.height=H+'px';
document.getElementById('capa').style.top=(pagina[1]/2)-(H/2)+pagina[3]+'px';
document.getElementById('capa').style.left=(pagina[0]/2)-(W/2)+pagina[2]+'px';
}
function cerrar(){
document.getElementById('capa').style.left='-1500px';
}
</script>
</head>
<body>
<form action="" method="get">
<input type="button" value="abrir" onclick="abrir(200,300)" />
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<label for="Submit"></label>
<input type="button" name="Submit" value="abrir" id="Submit" onclick="abrir(400,300)" />
</form>
<div id="capa" style="background-color:#F00; position:absolute; left:-1500px" onclick="cerrar()">click para cerrar</div>
</body>
</html>