iChat Version 4: A Brief review and What's changed.
iChat made it's it way into the Apple Application fold in about 2003 with the first version. We are talking at the time of Jaguar (10.2.x).
At that point it was just a basic AIM client. That means that Apple developed an application that worked with other Clients that use the AIM Service. They came to an agreement with AIM that @mac.com email IDs would be recognized by the AIM Servers as valid AIM screen names (See iChat 4 section about changes to @mac.com/.mac).
So iChat (ver 1) can Text chat (including Group chats) and send Files and Pictures to other AIM based clients
Then along came iChatAV (iChat vers 2). It came initially as a Beta and then as a $29.00 Add-on application for 10.2.x (Had to be 10.2.5 or above though). What it added was the ability to do Audio only and Video Chats with similar equipped Buddies (AIM went A/V for PCs around the same time). It was free with Panther (10.3.x).
At iChat 3
iChat 3 added Multichating to Video and Audio only chats. It also adds a much improved Group system in the Buddy list allowing them to be displayed in Groups.
Multi-Video chats can be between up to 4 buddies (you and three others). Audio Only chats can be between up to 10 Buddies.
iChat 3 also added the ability to use Jabber IDs creating a third Buddy List that could be on view. If you had a Googlemail ID and enable GoogleTalk you could use this in iChat.
A note about Passwords with Apple Screen Names
As with other versions of iChat the Password for any Screen Name has to be 16 Characters or less to be accepted by the AIM Servers for a Log in. As @mac.com (and the newer @me.com) passwords can be longer, this needs to be watched.
iChat 4 Adds
The ability to share you files as the Live Video feed with iChat Theater or slide shows of Pictures with a link to iPhoto.
The ability to allow your Screen to be Shared (you and your Buddy can navaigate around your computer) or to Share your Buddies Screen. This comes with an Audio chat at the same time so it is great for Teaching your mates something.
You can login multiple AIM valid names (@Mac.com, MobileMe and AIM) and Jabber IDs at once. It does however create as many Buddy List as you have Screen Names.
Text Chats can be brought into one window that then has Tabs.
And most dramatically it has Effects and Backdrops in the Video Chats.
Functions, Pictures and How-tos The Pictures and How-to Links are Indexes of more pages.
As well as these Pages here, help can be found at the Apple Discussion Boards This link is to the Front Index page.
A Word about Navigating the Apple Discussion Boards
The Boards are hierarchical. You can see from the URL of the page linked that it has the word "category" as part of the URL. The links onwards to the Forums are shown with folders on the Index page. What you will find is that there is often another category level to go through. For instance iChat AV links to here which still has"category" in the URL. At the top of this page are two links but they do not show folders at this Level. (below is a list of Topics to have the most recent posts in them - not all categories do this) These are to the actual Forums (iChat 1 is with iChat 2 and Earlier) where "forum" appears in the URL.
You can not post until you are in a Forum where the New Topic link is or have clicked on a Topic. You also have to be registered with Apple. Apple uses a common ID for iTunes, the Store and the Discussion - so you may have one already.