The latest version of iChat allows you to use Google Talk as a chat client. To configure this, go to the menu bar with iChat open and select: iChat -> Preferences... and then select the Accounts tab. Select the plus sign (+) below the list of accounts, and when the new account dialog opens select Google Talk Account as the Account Type. Once you select that, you'll get fields to enter your Google Talk account information. Now when you open/use iChat, you'll be able to chat with your friends who use Google Talk.