On the 'ME' line of newsfeeds, do something like:
That one will drop articles both from news1.acsi.net and from the udp.ME/news1.acsi.net,asciudp\ :*,!control,!junk\ ::
If you just want to not feed them to your peer, you'd do the same sort of thing on their line in newsfeeds:
and that'll do it.news.somepeer.net/news1.acsi.net\ (rest of feed stuff)ctlinnd reload newsfeeds 'aliasing out acsi'
The above is for INN and should be true for the old Netscape news server (which is INN in disguise). It's no doubt different for other software.