AJAX form validation

Hi,
I am currently validating a form client side only using javascript. People have started submitting blank forms by disabling javascript in there browser so i would now like to add some server side validation. Here is the code i am using. Any suggestions are welcome.

Thanks

javascript code

<script type="text/JavaScript">
  <!--
  function ValidateForm (FormName) {
  // check that a title has been selected
  if (FormName.Title.selectedIndex < 0)
  {
  alert("Error - You must select a title");
  FormName.Title.focus();
  return (false);
  }
  
  // check if the first drop down is selected, if so, invalid selection
  if (FormName.Title.selectedIndex == 0)
  {
  alert("Error - You must select a title");
  FormName.Title.focus();
  return (false);
  }
  
  // check to see if the first name is blank
  if (FormName.FirstName.value == "")
  {
  alert("Error - You must enter a first name.");
  FormName.FirstName.focus();
  return (false);
  }
  
  // check to see if the first name is blank
  if (FormName.Surname.value == "")
  {
  alert("Error - You must enter a surname.");
  FormName.Surname.focus();
  return (false);
  }
  
  // check if email field is blank
  if (FormName.Email.value == "")
  {
  alert("Error you must enter a valid email address.");
  FormName.Email.focus();
  return (false);
  }
  
  // Check email address contains @ and .
  var chkEmail = "@.";
  var chkStr = FormName.Email.value;
  var EmailValid = false;
  var EmailAt = false;
  var EmailPeriod = false;
  for (i = 0; i < chkStr.length; i++)
  {
  ch = chkStr.charAt(i);
  for (j = 0; j < chkEmail.length; j++)
  {
  if (ch == chkEmail.charAt(j) && ch == "@")
  EmailAt = true;
  if (ch == chkEmail.charAt(j) && ch == ".")
  EmailPeriod = true;
  if (EmailAt && EmailPeriod)
  break;
  if (j == chkEmail.length)
  break;
  }
  // Found @ and . in the email address
  if (EmailAt && EmailPeriod)
  {
  EmailValid = true
  break;
  }
  }
  if (!EmailValid)
  {
  alert("Error - The email address must contain a @ and a .");
  FormName.Email.focus();
  return (false);
  }
  // check to see if the contact telephone is blank
  if (FormName.Telephone.value == "")
  {
  alert("Error - You must enter a contact telephone number.");
  FormName.Telephone.focus();
  return (false);
  }
  
  // check that the agree terms has been selected
  if (!FormName.AgreeTerms.checked)
  {
  alert("Error - You must agree to the terms and conditions");
  return (false);
  }
  // check to see thatthe spam filter has been entered
  if (FormName.SpamFilter.value == "")
  {
  alert("Error - Please enter the spam filter ");
  FormName.SpamFilter.focus();
  return (false);
  }
  // check to see that the spam filter is correct
  if (FormName.SpamFilter.value != "19")
  {
  alert("Error - Incorect answer for the spam filter 20+6-7=");
  FormName.SpamFilter.focus();
  return (false);
  }
  return (true);
  }
  //-->
</script>