Google chat is available both in orkut and gmail, many people use google chat from either orkut or from gmail interface but it happens that some times that when you login to gmail or orkut you may see some annoying and disturbing chat windows with some offline messages or you might not want to chat with people via these interfaces.
In order to stop these annoyances you will need logout of google chat and once you logout you wont see any messages the next time to login
You can easily sign out of chat, just by clicking the link to sign out of google chat as shown in the image below
Or else you can disable the chat in gmail or orkut to get rid of it completely. In case of gmail, you will see the link at the bottom center of the page saying turn off chat if it is enabled.
In case of orkut you can disable chat by following the procedure below.
1. Click chat window to expand it, then click the options as shown in the image below
Now select the option sign out of chat as shown in the image below