function m_win(url,windowname,width,height){
   var features="location=no,menubar=no,status=yes,scrollbars=yes,resizable=yes,toolbar=no";
   if(width){
      if(window.screen.width>width)
         features+=",left="+(window.screen.width-width)/2;
      else width=window.screen.width;
      features+=",width="+width;
   }
   if(height){
      if(window.screen.height>height)
         features+=",top="+(window.screen.height-height)/2;
     else height=window.screen.height;
     features+=",height="+height;
   }
   window.open(url,windowname,features);
}