var myPopup;
function popup(url,h,w){
        if (popup.arguments[1]){
                myWidth=popup.arguments[1];
        }
        else
                myWidth=w;
        if (popup.arguments[2]){
                myHeight=popup.arguments[2];
        }
        else
                myHeight=h;

        if(screen.width > myWidth){
	        myLeft=(screen.width-myWidth)/2;
	}
	else
	    myLeft=10;

        if(screen.height > myHeight){
                myTop=(screen.height-myHeight)/2;
        }
	else
	    myTop=10;

        if(myPopup){
                myPopup.close();
        }
        myPopup=window.open(url,'myWin','toolbar=no,status=no,resizable=yes,menubar=no,scrollbars=yes,width='+myWidth+',height='+myHeight+',top='+myTop+',left='+myLeft+'');
        myPopup.focus();
        return  myPopup;
}