//controlla il sistema operativo
function isOS(os){
 osb=os.toLowerCase()
	agent=navigator.userAgent
	agentb=agent.toLowerCase()
	if (agentb.indexOf(os, 0)!=-1){
	 return true
	 } else {
	 return false
	 }
	}

//controlla se si utilizza netscape
function isNs(){
	if (navigator.appName == "Netscape") {
	  navVersion=navigator.appVersion
     vernumber=navVersion.split(" ");
      if (parseFloat(vernumber[0])<5)
			return true
	}
	return false
}

function isIE(){
 if (document.all)
  return true
 else
  return false
}

function isNs4(){
 	if (navigator.appName == "Netscape") {
	  navVersion=navigator.appVersion
     vernumber=navVersion.split(" ");
      if (parseFloat(vernumber[0])<5)
			return true
	}
	return false
}

function isIE4(){
 if (document.all) {
  if ( navigator.userAgent.indexOf("MSIE 4", 0)!=-1 ){
    return true
	}
  }
   return false
 }
 
 function isIE5(){
 if (document.all) {
  if ( navigator.userAgent.indexOf("MSIE 5", 0)!=-1 ){
    return true
	}
  }
   return false
 }