function validate_options_form(product_id)
{
    f=$('options_form');    

    p_f = $('proof_for_' + product_id);
    
    if (p_f.checked == true)
    {
        p_email = ($('proofEmail').checked) ? "an email address" : false;
        p_fax = $('proofFax').checked ? "a fax number" : false;

        if ((p_email) || (p_fax))
        {
            if ($('proofInformation').value == '')
            {
                alert("Please provide " + (p_email||p_fax) + ".");
            } else {
                return true;
            }
        } else {
            alert ("Please choose a proof method.");
        }
    } else {
        return true;
    }

    return false;   
}