function validateEmail(address) {
  var reg = /^([A-Za-z0-9_\-\.])+\@([A-Za-z0-9_\-\.])+\.([A-Za-z]{2,4})$/;
  if(reg.test(address) == false)
    return false;
  return true;
}

function checkContactForm() {
  if(document.getElementById('first_name').value == '') {
    alert('Please enter your first name.');
    document.getElementById('first_name').select();
    return false;
  }
  if(document.getElementById('last_name').value == '') {
    alert('Please enter your last name.');
    document.getElementById('last_name').select();
    return false;
  }
  if(validateEmail(document.getElementById('email_address').value) == false) {
    alert('Please enter a valid email address.');
    document.getElementById('email_address').select();
    return false;
  }
  return true;
}