404 Handler

As Chris said, the 404 handler page shouldn't return a 404 itself. Though if this is something you can to implement and you can't change the status, you could save the URI in HTTP_REQUEST and then not redirect to the 404 page if the request is for it already.

when HTTP_REQUEST {
   set uri [HTTP::uri]
}
when HTTP_RESPONSE {
   if { [HTTP::status] == 404 and $uri ne "/404.html"} {
      HTTP::redirect "http://www.example.com/404.html"
   }
}

Aaron