function jsCallback(scriptname,params,callback)
{
 var head    = document.getElementsByTagName('head').item(0);
 var oldhead = document.getElementById('lastloaded');
 if (oldhead) 
   head.removeChild(oldhead);
   
 script = document.createElement('script');
 script.src = 'callback.php?mod='+ scriptname + "&callback=" + callback + "&" + params;
 script.type = 'text/javascript';
 script.defer = true;
 script.id = 'lastloaded';
 void(head.appendChild(script));
}