This will show you how to talk to your friends who use google talk / gtalk using your ichat

this one is pretty easy.

open ichat
goto preferences
goto accounts
hit the + in the bottom left
account type: google talk
account name: username@gmail.com / username@googlemail.com
open server options
server: talk.google.com (should be there already)
port: 5222 (should be there already)
done. log in and talk to your gtalk buddies