For Mac I would also rec Colloquy like Lara said, but just in case there are any problems with that (though there shouldn't be), there is also another great program called Snak that has a 30 day free trial. I've used both and found them both pretty equally good (but Colloquy is completely free, where Snak is not).

Thanks to Cat for my rockin' avatar!
++++
(About Lois & Clark)
Perry: Son, you just hit the bulls eye. It's like we're supporting characters in some TV show and it's only about them.
Jimmy: Yeah! It's like all we do is advance their plots.
Perry: To tell you the truth, I'm sick of it.
Jimmy: Man, me too!