I just tested the two of them, but
www.jpilot.com seems the best solution for what I need to do, an IRC chat on our intranet.
Another very good script I have seen is PhPChat at
www.hotscripts.com. Unfortenately it uses some function that are not available under Windows, so I cannot use it. But I have seen this PhPChat working and it is very nice, also fully configurable, even more than jpilot, because you have access to the full source code!!!!