function popup(url, popupName, width, height, scrollbars, resizable, menubar) {
	
	if (width == undefined) width = 1000;
	if (height == undefined) height = 620;
	
	scrollbars = scrollbars ? 'yes' : 'no';
	resizable = resizable ? 'yes' : 'no';
	menubar = menubar ? 'yes' : 'no';
	
	var x = Math.round((screen.availWidth  - width) / 2);
	var y = Math.round((screen.availHeight - height) / 2);
	
	return window.open(
	    url,
	    popupName,
	    'left=' + x + ', top=' + y + ', ' + 
	    'scrollbars=' + scrollbars + ', ' + 
	    'resizable=' + resizable + ', ' + 
	    'width=' + width + ', ' + 
	    'height=' + height + ', ' + 
	    'menubar=' + menubar
    );

}