You need to be more specific with your question, which version of Mac OS are you running?
You should check out: https://discussions.apple.com/thread/1712458?start=0&tstart=0
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open ichat. click 'ichat' and then 'preferences' then click 'accounts' there should be a + sign, click that to make a new account
"You cannot use ichat for Windows. Ichat is used with Mac, but you can use AIM with Windows and comunicate with Ichat on Mac. You will also need internet."
It switches on automatically when the Photobooth or iChat apps are opened.
Just open iChat and log in with your Google Talk account - works great!
You have to get a mac book laptop or desktop
iChat can be dowloaded at versiontracker.com. http://www.versiontracker.com/dyn/moreinfo/macosx/16887
iChat uses the AIM network so a Windows user with an AIM account (See links below) will be able to contact a Mac user with iChat.
iChat is not an available feature on the iPod Touch. There is facetime for the new iPod Touch (fourth generation), but iChat is strictly for Mac laptops and desktops.
iChat is provided free with all Mac computers (See links below) and can be installed from the Mac OS X installation discs. It is not legally available from any other source.
You can only do this of you have a mac with ichat
u need a mac computer to open the mac app store
You cannot install iChat on your computer if you are not running Mac OSx. However if you install AIM you will be able to chat with iChat users.