At the Tiger (10.4) release of the OS, iChat 3 came out with the name drop of the AV suffix. This was not interchangeable with earlier versions of the OS. At iChat 3 Apple Added the Jabber Option. This increased the Services that iChat could join. With careful selection of your Jabber Server you could find one that has "Transports" to add connectivity to the MSN and Yahoo services as well as plain Jabber Buddies. The OS X Server added a iChat Server that is in fact a Jabber server. GoogleTalk or rather GoogleMail IDs can be made to work.
This was when Add-ons of all sorts took off for iChat.
The Preferences were then Changed to Match
iChat version 3 (the AV was dropped from the name)
The General Section has pretty clear indications about what each item does.
The first option of apparently Remaining On-Line as it were when Logged out seems to be the one most difficult to prove as to whether it works as iChat always sees other iChat Buddies as On or Off-Line.
The Shapes selection changes the coloured blobs that indicate Green as Available, Red as Away and Amber as Idle to Shapes. At this point they lose the 3D-ness of the rounded normal default blob.
Next is the option to deplay the Menu Bar icon. This is a grey speech bubble that appears to the right hand side of the Menu Bar towards the Clock side.
Auto-Relpy is a feature that picks out any Away Status Message and responds with it when Away is Set in the Buddy List.
Panther has Fast User Switching and this allows you to have several User Accounts open on the same Mac. Setting this to Remain on Line means thee Users can Bonjour each other (or rather leave messages when the account is Switched back).
The What does iChat Do when waking from sleep is a series of Raido Check boxes.
Lastly in the General Section is the choice where to send Downloaded files to. By Default this is the Desktop. The actual function varies when in a Text chat. when it is always the Desktop. Files accepted from a Buddy that is not in a Text chat do go to the folder selected.
The Screen Name adding became more intuative and requires that you use the Add button to addNew Screen names and the list to change between them. It added tabs to the right for the Server Settings (Previously a button called Server Options in iChat 2).
The Server Settings tab allows you to change the Server Name and Ports. AIM used to have different servers that would allow iChat to Login but only login.oscar.aol.com remains. The Port can be changed and some modems and routers prefer that it is different. What this means is that as iChat uses port 5190 on the TCP Login and the UDP File Sending and some devices do not like this dual use of the port. The most common suggestion on the Apple Discussions is to use port 443 as this is below the NAT threshold of 1024 and is separate from the UDP use of port 5190 that can not be changed.
The Secruity tab replaces the whole Privacy Pane of iChat 2. It has options of who can contact you. It can Block everyone, Block some (has List to add or remove), Allow Buddy List Only and Allow All.
The Messages Pane changes very littile between the verions. It lets you choose your Font, Style if the Font has Options, Bubble Colour and Font Colour. Choose either Light on Dark or vice versa as the colours. Try not to choose things that clash. Remember in a long chat your Buddy is going to have to look at at it. You can choose to overide your incoming Buddies Choices.
An Important choice here is also the option to Save Transcripts Automatically. I would strongly recomment this. It will save group chats as well as ordinary ones. Where Pictures have been sent in the Chat these are still viewable although they can not be dragged to the Desktop as they can in a Live Chat. (Dragging a chat Bigger expands the Pic to as close to Full size as your Screen allows if it is really big.)
I have included a shot of a Video Pic created in iChat 4 but can be done in earlier versions with ChatFX, an Add-On. Essentailly this pane allows you to choose the Mic if you have multiple input devices. The Bandwidth iChat uses can be capped here. This may be useful if you want to do other things with your Internet Connection. In iChat 2 iChat is fairly greedy in this respect, grabbing about 80% of what you have. This means it can be effected by other apps or computers using the Internet.
If you have multiple cameras youyou get a drop down for this.
The Chax Pane is created when Adding an Add-On called Chax This is for iChat 3 and above. It adds a pane that has it's own tabs. It can group text chats into a tabbed set up that iChat 3 can not do itself. It can be used to set Auto Responding to Video and Audio chats.
The Buddy List
This has your Buddy Name on the left which can be toggled between your Address Book Name and the Screen name.
On the Right is you Buddy Pic. This can be Clicked and used as a Drop down to select an older previous choice or navigate to a new selection from anywhere on your Hard Drive. The Default folder is Apple's range of alternative Buddy Pics (to the ones in the Accounts Pane of the System Preferences).
Just to the left of that is the Video or Audio Icon dpending if you have a Camera and/or a Mic .
It is currently showing what is reffered to as the Stacked version.
This mean this person can join (at least) chats with several Buddies (3 others in Video and 9 others in Audio Only chats)
As you can see some of the Buddies show the Flat icon meaning that can only do 1-1 chats.
The Grey text are the Status Messages and the "Mobile" option is US only at present.
This Buddy List has Groups Displayed. As you can pick out some have leading Characters to get around the limits of the Alphabet.
One of the things the Chax Add-on can do is change the Bars for the Goups and the Fonts for the Buddy List.
The Coloured "blob" style markers to the left of each Buddy indictes if they are Avialable, Idle or Away. These can be changed to Shapes in the iChat > Preferences > General Section.
About iChat
iChat is an Instant Message and Video and Audio only chat application.
It uses the AIM Service as the Text message part but from version 3 onwards can also join Jabber servers including GoogleTalk.
It can send Files and Pics to other iChat Users and in certian circumstances the Pics are displayed in the Chat window.
In later versions it can have add-ons that enhance video features that have then been somewhat included by Apple in Version 4
