function chkForm(frm) {
  // the name of the form
  f = frm;

  // change msg to the name of any field you want to make required.
  if (f.card_type) {
    if (f.card_type.value == '') {
      alert('Please select your card type.');
      return false;
    }
  }
if (f.card_number) {
    if (f.card_number.value == '') {
      alert('Please enter your card number.  Visa and Mastercard have 16 Digits, and Amex cards have 15 digits.');
      return false;
    }
  }
if (f.exp_date) {
    if (f.exp_date.value == '') {
      alert('Please enter your card expiration date in the following format. (MM/YY)');
      return false;
    }
  }
if (f.security_no) {
    if (f.security_no.value == '') {
      alert('Please enter your 3 digit security code located on the back right of your card.');
      return false;
    }
  }
if (f.name) {
    if (f.name.value == '') {
      alert('Please enter your name exactly as it appears on the card.');
      return false;
    }
  }
if (f.address) {
    if (f.address.value == '') {
      alert('Please enter the address that your card statement is delivered to.');
      return false;
    }
  }
if (f.amount) {
    if (f.amount.value == '') {
      alert('Please enter the payment amount you would like to make.');
      return false;
    }
  }  
if (f.email) {
    if (f.email.value == '') {
      alert('Please enter a valid email address.');
      return false;
    }
  }  
}