If you read your Gmail email in a web browser like Firefox, you can talk to your friends using Gmail's built-in chat (in the lower left of the screen). You can also use a client like Spark or iChat.
Read an overview of Google Chat to get started!
Chat with your friends in a web browser like Firefox (by going to go.brandeis.edu/gmail and using Gmail's built-in chat) or use a program like Spark or iChat. Compare different clients or select your client of choice for setup directions: