Dovrei controllare un form in JS in cui tutti i campi sono obbligatori, mi aiutate?

codice:
<head>
<script language="JavaScript" type="text/JavaScript">
<!--
function MM_findObj(n, d) { //v4.01
  var p,i,x;  if(!d) d=document; if((p=n.indexOf("?"))>0&&parent.frames.length) {
    d=parent.frames[n.substring(p+1)].document; n=n.substring(0,p);}
  if(!(x=d[n])&&d.all) x=d.all[n]; for (i=0;!x&&i<d.forms.length;i++) x=d.forms[i][n];
  for(i=0;!x&&d.layers&&i<d.layers.length;i++) x=MM_findObj(n,d.layers[i].document);
  if(!x && d.getElementById) x=d.getElementById(n); return x;
}

function MM_validateForm() { //v4.0
  var i,p,q,nm,test,num,min,max,errors='',args=MM_validateForm.arguments;
  for (i=0; i<(args.length-2); i+=3) { test=args[i+2]; val=MM_findObj(args[i]);
    if (val) { nm=val.name; if ((val=val.value)!="") {
      if (test.indexOf('isEmail')!=-1) { p=val.indexOf('@');
        if (p<1 || p==(val.length-1)) errors+='- '+nm+' must contain an e-mail address.\n';
      } else if (test!='R') { num = parseFloat(val);
        if (isNaN(val)) errors+='- '+nm+' must contain a number.\n';
        if (test.indexOf('inRange') != -1) { p=test.indexOf(':');
          min=test.substring(8,p); max=test.substring(p+1);
          if (num<min || max<num) errors+='- '+nm+' must contain a number between '+min+' and '+max+'.\n';
    } } } else if (test.charAt(0) == 'R') errors += '- '+nm+' is required.\n'; }
  } if (errors) alert('The following error(s) occurred:\n'+errors);
  document.MM_returnValue = (errors == '');
}
//-->
</script>
</head>

<body>
<form name="contatti" method="post" action="" onsubmit="MM_validateForm('email','','RisEmail');return document.MM_returnValue">
  <table width="335"  border="0" cellpadding="0" cellspacing="0">
    <tr>
      <td class="txt">nome e cognome</td>
      <td class="txt">email</td>
    </tr>
    <tr>
      <td><input name="cognome" type="text" id="cognome"></td>
      <td><input name="email" type="text" id="email"></td>
    </tr>
    <tr>
      <td colspan="2">messaggio</td>
    </tr>
    <tr>
      <td colspan="2"><textarea name="messaggio" cols="64" rows="7" id="messaggio"></textarea></td>
    </tr>
    <tr>
      <td colspan="2">Come ci hai trovato?</td>
    </tr>
    <tr>
      <td colspan="2"><input name="motori" type="checkbox" id="motori" value="checkbox" /> 
        Motori 
        <input name="link" type="checkbox" id="link" value="checkbox" />
        Link 
        <input name="specificare" type="text" id="specificare" style=" value="specificare" size="30" />        Altro</td>
    </tr>
    <tr>
      <td colspan="2"></td>
    </tr>
    <tr>
      <td colspan="2"> [img]/images/reset.gif[/img]
          <input name="Invia" type="image" value="Invia" id="Invia" style="border : 0" src="/images/invia.gif" width="44" height="16" border="0" />
          

</p></td>
    </tr>
  </table>
</form>
</body>
</html>