function popupwindow(url,h,w)
{
	var xpos = screen.availWidth/2 - w/2; 
	var ypos = screen.availHeight/2 - h/2; 
	window.open(url, "", "toolbar=no,menubar=no,scrollbars=yes,resizable=yes,location=top,status=no,width="+w+",height="+h+",ScreenX=0,ScreenY=0,Top="+ypos+",Left="+xpos); 
}