//pop up a window
function popit(address, winname, popW, popH) {
		var w=800, h=600;
		if (window.screen) {
			w = screen.availWidth;
			h = screen.availHeight;
		}
		var leftPos = (w-popW)/2, topPos = (h-popH)/2;
		window.open(address,winname,'width=' + popW + ',height=' + popH + ',top=' + topPos + ',left=' + leftPos + ',scrollbars=0,resizable=0,toolbar=0,directories=0,location=0,menubar=0,status=0');
}