function preview(URLtoOpen, windowName,wi,he, windowFeatures) {
	var winl = (screen.width-wi)/2;
	var wint = (screen.height-he)/2;
	var 	Features='height='+he+',';
		Features+='width='+wi+',';
      		Features+='top='+wint+',';
		Features+='left='+winl+',';
		Features+=windowFeatures;
	newWindow=window.open(URLtoOpen, windowName, Features);
    }

<!-- (script type="text/JavaScript" src="includes/popup.js") (/script) -->
<!-- (a href="javascript:preview('URI','preview','730','500',toolbar=no,scrollbars=yes');") -->