AS the other poster has pointed out ichat 101 is a good place to start.
Some History.
When Appl decided to create a IM application they had to decide to either join an existing IM service or create there own.
They decided to join AIM/AOL and had @mac.com Email/Account names recognised as Valid AIM Screen names. iChat became an AIM client.
This meant you could use an AIM name you already had or a new one if you did not have an @Mac account or add a @Mac account ID as your Screen name.
Although whichever name you have iChat will create a Buddy list that you can add those people with AIM valid name (An AIM Buddy List) - it has always had the ability to distinguish whether you are adding an @Mac valid ID separate from an AIM name.
There issues currently if you have a newer MobileMe name which is normally an @me.com name.
You tend to have to add this as if it were an AIM sort of Screen name and add the suffix as you do so (most AIM names don't come with an @something.com suffix but some do and the @ is a valid character)
At iChat 3 a Separate Buddy list was added to use Jabber IDs with.
as GoogleTalk is a Jabber server you can add this as your Jabber ID
iChat 4 takes this a stage further and splits GoogleTalk and Jabber like it splits the @mac and AIM types of names.
SO when you choose in iChat > Preferences > Accounts and use the plus button later to add more Screen names you get this drop down in iChat 4
The potential for the Bonjour Buddy list is there all the time as iChat can if you enable the Bonjour account look for and find other Macs running ichat on your LAN. This Buddy List will identify you by your Address Book details and will do the same for your Buddies.
It does mean however if the computers are your you can not be "Fred Flintstone" on both computers as this does not work.
On to Adding Buddies.
Once you have set up iChat with at least one Screen name you can add Buddies to that list.
At the bottom of the Buddy List is a plus Button (Except the Bonjour one)
Using the Plus button will get you at least an option to Add Buddies (in some versions Add Groups is also here).
If you have to select Add Buddies do so.
You then get a screen to type in the Screen name and "Real Name" of the Buddy.
If you are adding to a AIM valid List you also get the option to add then as either AIM or @Mac
You need to choose the right one.
The @mac ones need only the bit before the @Mac.com bit as the iChat software adds this for you. (AIM Names don't normally have a @something.com bit)
If adding to the Jabber List you do not get the same distinction between GoogleTalk and other Jabber IDs
I am not sure where you are seeing Services.
Can you explain the steps taken to get where you see that so I can explain it further ?
Once we have sorted that I will look at the icons issue.
10:48 PM Tuesday; August 5, 2008