Start Kopete.
Choose Settings->Configure...
Select Accounts from the left navigation bar.
Select New...
The screen should appear like this one.

The next screen should be like the one shown below:

In the Jabber ID, enter your complete google account ID. For eg, I would enter jitendra.harlalka@gmail.com for me. Choose Remeber Password as per your convenience. In case you choose it, provide Password in the TextField. Similarly, you can choose Exclude from connect all and Exclude from Global Identity as per your convenience.
Now, choose Connection tab. It should look like this one.

Check Use protocol encryption (SSL) and Override default server information. Type talk.google.com in the Server TextField. Keep Port to 5223. Click Next.
Choose color for your google talk ID. Click Finish button. You should find yourself online if you are connected to internet connection.