"Mac Pro" tell me it is an intel machine.
That means at least Leopard (OS X 10.5.x)
That means iChat version 4.x.x at least
That in turn menas you have the ability to add Jabber IDs to iChat and more specifically there is a a specific Googletalk option.
Go to the App Menu Item > Preferences Accounts
IN there you will find a List (It may only contain Bonjour at the moment).
CLick the + icon/Button under the list, lower left.
In the new pane the top item is a drop down.
It will list AIM (And the Apple, AIM Valid names) the Google and Jabber beneath a line.
If you have a Googlemail ID and have Enabled "Talk" on your Google setting you can chose Google Talk and enter your Google Mail ID as it is shown to your on the Web Mail Page (It makes a difference if it ends @gmail.com or @googlemail.com)
Add the password.
A Buddy List will appear (with any Buddies you have added at Google) and it will appear in the list of Account in the Preferences.
In the Server Settings tab it will read port 5223 and the server name will be talk.google.com
You are ready to chat to existing Buddies or add new ones.
Please, if posting Logs, do not post any Log info after the line "Binary Images for iChat"
iMac 2.5Ghz 5i 2011 (Mountain Lion 10.8.2)
G4/1GhzDual MDD (Leopard 10.5.8)
MacBookPro 2Gb (Snow Leopard 10.6.8)
Mac OS X (10.6.8),
Couple of iPhones and an iPad
"Limit the Logs to the Bits above Binary Images." No, Seriously