As an author of RichMemo, let me clarify - there was never Qt implementation (patches are welcomed. and it
seems it should not be complicated for developers with good Qt-Pascal knowledge). But having RichMemo compiled for Qt makes me a bit surprised.
If you're looking for chat functionality (thus no editing abilities)
There's TRichView implementation for Lazarus:
http://wiki.freepascal.org/RichViewAnother options is
lzRichEditI'm not sure if either is working for Qt.
You could try using SynEdit for the chat as well (though it's not really suitable, since it's fixed-width oriented)