IChat only works on macs as far as I know. It could probably be run using an emulator but then that gets a little complicated.
I personally find ICQ complicated and not as simple as AIM. I dont know anyone that uses it so I dont really have a use for it either. I guess it is better than AIM as far as features. If you wanna give it a try, I suggest using ICQ Lite instead of the full version. The full version is much too complicated and bloated.