Hi,
Lets check the steps
With iChat open go to the iChat Menu > Preferences > Accounts
In the Accounts use the + icon at the bottom of the list (Should have at least Bonjour in there)
Click and hold the top item in the new pane and it should reveal several options, one of which is Google.
Select Google.
Add your Google Name as it appears when you go to Google Mail Web Site.
It makes a difference if you account ends @googlemail.com and you enter @gmail.com
NOTES
You should have already been to Google and enabled Talk on your Google Account settings
You can only use a Google Mail Account (either ending) outside ot the Google web pages. (Other Google accounts can have Talk enabled but you can't sing in from other apps.)
Next
Now that the Google Account is set up then go to the sever settings tab
This should list the server as being talk.google.com
It will normally be an SSL Login using port 5223
You can change the port if you go to the Account info tab an untick the "Enable this Account" box to Log out.
Then items in the Server Settings fields can be edited.
Try port 443
Summary
Make sure it is a Google Mail Account
Make sure the Talk option is enabled in your Google Account Settings.
Double check you are using the Google option in the iChat Preferences to add accounts.
Check the Server name afterwards and possibly change the port.
9:44 PM Tuesday; April 17, 2012
Please, if posting Logs, do not post any Log info after the line "Binary Images for iChat"
iMac 2.5Ghz 5i 2011 (Lion 10.7.3)
G4/1GhzDual MDD (Leopard 10.5.8)
MacBookPro 2Gb (Snow Leopard 10.6.8)
Mac OS X (10.6.8),
"Limit the Logs to the Bits above Binary Images." No, Seriously