"Portal" is not a pre-defined namespace. You need to define it. Then
it should work.
see
http://www.mediawiki.org/wiki/Manual:Namespace .
ps: this query is best for the mediawiki-l list, not wikitech-l. :)
cheers
Brianna
--
They've just been waiting in a mountain for the right moment:
http://modernthings.org/