Anyone know a good configurable chat site?

A group of people I know want to set up a chat room. They’ve bandied about things like AOL or Yahoo IM, both of which can be used to set up chat conferences. The big problem with them is that it’s impossible to get everyone on one server - some people use AOL, some use Yahoo, some use MSN IM, you get what I mean.

On the other side of the spectrum, I know I can set up chat software on my Web hosting site, and can configure any way I want. For various reasons I don’t want to do this - primarily because I’m not sure I want to be responsible for the group’s chat needs for the rest of my life.

So what’s the middle ground? I know about IRC, but I shy away from it because 1) I don’t know if there’s a decent browser-based client for it and 2) the learning curve is high for the non-computer-literate.

Can anyone recommend a chat server/service/doohicky that:

1 - is Web based. Downloading a client is a hassle.
2 - isn’t too techie
3 - doesn’t require a whole pile of registration
4 - is free, but doesn’t kill you with popups or other advertising. A little advertising I can deal with. A lot, no way.

bump. Anyone?

Only thing that comes to mind is Trillian. I’ve never used it so I’m not sure if it meets your four prerequisites but from what I understand it’s supposed to bridge the gap between all those different chat clients you mentioned.