function popup(url, popW, popH, wname)

{
var w = 640, h = 480;
if (document.all || document.layers) {
	w = screen.availWidth;
	h = screen.availHeight;
	}
var leftPos = (w-popW)/2, topPos = (h-popH)/2;
var popupWin = window.open(url, wname, 'toolbar=0,location=0,directories=0,status=0,menubar=0,scrollbars=0,resizable=0,width=' + popW + ',height=' + popH + ',top=' + topPos + ',left=' + leftPos);
if (!document.all && window.focus)
	popupWin.focus();
}