Gmail includes a built-in chat gadget that you can use to send and receive instant messages with other people in your organization. And if you also want to hear and see the person you're chatting with, install the voice and video chat plug-in to start having real conversations right in your Gmail window (see instructions below).
What How to Use Gmail Chat:
Click the Chat icon at the lower left of your Gmail window. You can also resize the chat area by dragging its top divider line.