I've spoken with pcwzrd13 prior to posting this message and he has given permission for me to make this public.
I've been reading through later editions of the the UK's Dreamcast Magazine (Unofficial by Paragon Publishing) at archive.org. In issue 24 (July 2001), they did the following article that included screen grabs of the European Dreamarena Chat Rooms.
One the one hand, this is good as I have been unable to find any images of the old Dreamarena Chat Rooms on the internet. You can see the layout on the Dreamcast browser and names of some of the chatrooms that were available at the time (Ecco Pool & Sauna, Jazz Club, Swearbox 18+, Sin Bin). The images even show the URL they used with Dreamarena Chat (serv1.chat.dream-key.com). However the content of the chat itself is very explicit. It's very surprising something like this was even published in a Dreamcast Magazine! Anyway, here is a link to the magazine scan and the pages below showing the screens (pages 25-30). You need to use the zoom facility if you really want to read the content; the Swearbox chat room certainly lived up to its name!
For the record, I never used Dreamarena back in the day except to obtain the free copy of Chu-Chu rocket.