Chat Room, Discussion Collabrotative and Design Patterns ?

Hello,

We have been tasked to look into an implementation of simple web based
collaborative working between users. I have been searching for some
design patterns on Chat room, and discussion thread designs. But have
had limited success. I thought there would be web patterns for these,
since they are so common.

We do not need heavyweight solutions, just a lightweight web client/
server based solutions. Probably menas Java/ActiveX objects with
appropriate security mechanisms.

So any advice on appropriate designs and patterns would be good

Thanks

Jules