function popup (url, w, h, window_name) {
	var chasm = screen.availWidth;
	var mount = screen.availHeight;
	var ie = /msie/i;
	if (!w)
		var w = 500;
	if (!h)
		var h = 360;
	if (!window_name)
		var window_name = 'halfmoon';

	var features =
		'width=' + w + 
		',height=' + h + 
		',left=' + ((chasm - w - 10) * .5) + 
		',top=' + ((mount - h - 150) * .5) + 
		',scrollbars=yes'+
		',resizable=yes';
			
	if (!new_window) 
	{
		var new_window = window.open (url, window_name, features);
		if (new_window) new_window.focus();
	}
}