How to make gnus fetch news headers automatically

[Piotr Zielinski]

Hi,

Could you tell me how to implement the following functionality gnus?
For some groups (which I consider particularly important or
interesting) I would like to be notified about every new article,
including some of the headers like the subject and the author.  More
precisely, for each such article I'd like my elisp function to be
called with the current buffer containing all the headers of that
article.  I've somehow managed to do it for email groups (nnml) and
rss but I have no clue how to achieve the same with newsgroups.  I'd
be grateful for any suggestions.

Piotr