Use Chat to talk to two or more people at a time, instead of an Instant Message. This document applies to iChat 1.x and Mac OS X 10.2 or later.
Start a Chat window to talk to more than one person. A Chat is for "conference" conversations with many people, and Instant Message is for private conversations with a single person.
If you want to be able to add more participants later, then you should start your message as a Chat window instead of as an Instant Message window. To start a Chat, simply choose New Chat or New Chat with Person from the iChat File menu.
Tip: When naming windows, iChat does not distinguish between Instant Message and Chat type windows. To learn how to distinguish them, see "iChat: Chat Windows Not Named Correctly".