Try editting web.xml in:
Add elements like these (for example):
<error-page> <error-code>404</error-code> <location>/404.html</location> </error-page>
Review the Servlet spec. and/or the appropriate web.xml DTD or XSD for more info on configuring a webapp to deal with error codes.
Hope this helps.
Mh... it doesn't seem to work...
The problem is that I don't want the Portal answer me with a customized 404 Error page... I want a 404 HTTP error! Not a 200 OK HTTP answer with an error page... I don't know if I explain me...