function popupwindow(url, _w, _h)
{
	_w = Math.min(_w, screen.availWidth * .95);
	_h = Math.min(_h, screen.availHeight * .95);
	
	var oW = window.open(url, 'popup', 'width=' + _w + ',height=' + _h
						 + ',top=' + ((screen.availHeight - _h) / 2)
						 + ',left=' + ((screen.availWidth - _w) / 2)
						 + ',resizable');
	oW.focus();
}