I just found Adium and I am in chat-love. I can sign in to ALL of my chat accounts at once. Set-up is so easy. I was up in running in the amount of time it took to type in all of my accounts. Love. LOVE so far. Will let you know if I hate it after actually chatting with someone. Hee!
(I have Trillian on my windoze machine, but this is the first multiple account program I’ve seen for a Mac.)