If you prefer using Google Talk (GTalk) to chat online with your friends and only use Gmail to check emails and not for chatting. This tips will prove useful to you – This Tech Tip will help you to completely remove (and not just hide) the chat box from your Gmail mailbox.
Log on to your Gmail Settings page, switch to the Chat tab, choose “Chat Off” and click on the “Save Changes” button. Alternatively, you may use this link to directly access your Gmail Chat settings page. You can re-enable chat in your Gmail by using the “Chat On” option.