there is a free (open source) client on http://jwchat.sourceforge.net/ available with some minor bugs (search this forum for jwchat to read some bugs and possible setups). http://zeank.in-berlin.de/ is the page of the author, now with a new[/b] link to http://jwchat.org/MUCkl/ (MUCkl is a web-based application for groupchats). The author of the code did also write mabber http://mabber.com/ which is imho not open source.
Thanks for the spark.jnlp link, I have seen sun remote login console running via jnlp. So when I heard about spark jnlp option, I am hoping that this would be the answer to the web base client. Now that I can try it myself, it is far short of my expectation. I found out that it is literally downloading the client and it handles the connection itself and not via the server (jwchat handles connection through tomcat server). It seems like the only option will be to work on jwchat. Thanks for the info anyway.