function form_validation()
{
    valid = true;

    if ( (document.share_email_form.email_to.value == "") && (document.share_email_form.email_from.value == "") )
    {
        alert ( "Please fill in the 'Enter recipient\'s email address:' and 'Enter your email address:' boxes." );
        valid = false;
    }

    else {

    if ( document.share_email_form.email_to.value == "" )
    {
        alert ( "Please fill in the 'Enter recipient\'s email address:' box." );
        valid = false;
    }

    if ( document.share_email_form.email_from.value == "" )
    {
        alert ( "Please fill in the 'Enter your email address:' box." );
        valid = false;
    }

   }

    return valid;
}