function validateZipCode(zipField) {
        var zipField;
        zipField = document.getElementById(zipField);
        if (!isNaN(zipField.value))
        {
            if((zipField.value > 20000) && (zipField.value < 24700))
            {
                return true;
            }
            else
            {
                alert('We\'re sorry.  The zip code you have entered is outside of our service area.');
                zipField.value = '';
                zipField.focus();
                return false;
            }
        }
        else
        {
            alert('The zip code entered does not appear to be valid.  Please check the value and try again.');
            zipField.value = '';
            zipField.focus();
            return false;
        }
    }