Well I'm currently in developement of a replacement for MDX. It's called DCX and it isn't finished yet though. As a chat window thing I would imagine you could use a richedit control (which supports mIRC control codes but isn't finished yet) with a regular edit under to type the text. The richedit is readonly and I could check for the scrolling part to be added with a command on the richedit if that may interest you.
The DLL is currently beta but fairly advanced in the dev cycle. I have lots of plans for it adding advanced UI controls letting the users build nice functional GUIs for their projects.
If you want the URL you can pmsg me or search the forums, I think it was already posted in the past, I wouldn't want to pollute it again with unecessary spam.
