function checklogin(formName){

	var username;
	var password;
	var check;
	var what;

	check = true;
	what = "ie4"; //imposto il default a internet explorer

	if (document.layers) { 
		what ="ns4"; 
	} 
	else if(document.all) { 
		what ="ie4"; 
	} 
	else if(document.getElementById) { 
		what="dom1"; 
	} 
	else { 
		what="none"; 
	} 
	
	if(what=="ie4"){
		username = document.getElementById(formName).username.value;
		password = document.getElementById(formName).password.value;
	}
	
	if(what=="dom1"){
		username = document.getElementById('username').value;
		password = document.getElementById('password').value;
	}			

	if (username == null || username == ""){
		alert('username è indefinito');	
		check = false;
		return false;
	}

	if (password == null || password == ""){
		alert('la password è indefinita');	
		check = false;
		return false;
	}

	if (check == true){
		if(what=="dom1"){
			document.login.submit();
		}
		if(what=="ie4"){
			document.getElementById(formName).submit();	
		}		
	}
	else{
		alert('controlla user e password');
		return false;
	}	
}