You can activate chat on Orkut by clicking Sign into chat in Orkut home page.
You can see which friends are online by checking the chat roster on the bottom right side of your page. If the roster is minimized, just click on Online friends to maximize it for viewing.
How to enable chat?
To enable Orkut chat you just need to verify your e-mail address with us. Once you've verified your email address you'll be all set to chat on Orkut.