It won't work with other browsers unless you do some fiddling. Don't even know if it's possible with IE.
Regarding Trillian, read bugtraq. But if you want to insist on using it, then it can talk to IRC servers. Just go into your accounts and tell it to connect to irc.freenode.net as the server. And then join #openacs.
There's a link for IRC beginners at the openacs irc page.
On the integration issue, OpenACS is a server-side solution for web applications. Trillian is a client for multiple instant messaging protocols, and IRC. The AOLserver+Jabber integration was possible because Jabber also has a server. Not so with trillian.