function checkFields()
{ 
  if(document.bookform.first_name.value==""){
    alert("Please enter your First Name.");
    document.bookform.first_name.focus();
    return false;
  }

  if(document.bookform.last_name.value==""){
  alert("Please enter your Last Name.");
  document.bookform.last_name.focus();
  return false;
  }
  
  if(document.bookform.first_name.value==document.bookform.last_name.value){
    alert("First Name can't be the same as Last Name");
    document.bookform.first_name.focus();
    return false;
  }

  <!--phone-->

  if(document.bookform.phone.value==""){
    alert("Please enter your Phone Number.");
    document.bookform.phone.focus();
    return false;

  }
  <!-- end phone-->

  if(document.bookform.URL.value==""){
    alert("Please enter your URL.");
    document.bookform.URL.focus();
    return false;

  }

    if (document.bookform.email.value==""){
    alert("Please enter your email address.");
    document.bookform.email.focus();
    return false;
  }else if(document.bookform.email.value!=""){
    index=document.bookform.email.value.indexOf("@");
    if(index==-1){
      alert("Your have entered an invalid email address. Please check you email address.");
      document.bookform.email.focus();
      return false;
    }else{
      lastd=document.bookform.email.value.substring(index+1,document.bookform.email.value.length);
      if(lastd.indexOf(".")==-1){
        alert("Your have entered an invalid email address. Please check you email address.");
        document.bookform.email.focus();
        return false;
      }
    }
  }
}