function popup(url) {

	var w = 480, h = 340;

	if (document.all || document.layers) {
	   w = screen.availWidth;
	   h = screen.availHeight;
	}

	var popW = 600, popH = 600;

	var leftPos = (w-popW)/2, topPos = (h-popH)/2;

	var newPop = window.open(url,'popup','width=' + popW + ',height=' + popH + ',top=' + topPos + ',left=' + leftPos + ',scrollbars=1');
	newPop.focus();

}