"bog" as in use up a lot of memory? There's several programs that I use that work pretty good. I'm currently using
Slick and that's working out really good for me. My friend uses
beejive and swears by it. There's also
Palringo, but I haven't used that recently. They use to be good, but the thing about them is that they connect through their server to the IM's server so if their server is down (which was too often for me) then your IMs wouldn't go though.
Check it out, see what you like.
Edit: Accidentally said Agile Messenger when I meant to say Palringo.