[Mediawiki-l] Show articles of more than one category

[WikiPlant]

Hiho :)
Does anyone know how to write a special page and/or a (php?-)script 
where users can pick some categories (of all or a specific selection 
created by a sysop) and than a page shows all articles with the chosen 
categories? Sorry but I didn't find any information about that in the 
internet..
Thanks for your help! Florian :)