Great to hear there's another multiboxer!
Here's a couple sites to check out if you haven't found them already.
http://www.autohotkey.com/ -- I'm not sure if this works on macs, but it's a great program for helping control multiple characters on one system.
http://www.dual-boxing.com/ -- Great info site. This'd be the place to ask if you get stuck on something, chances are good someone's got an answer there.
Once you get used to multiboxing, there's no going back, it changes the entire game.
