I have a Gmail account. I have configure it with my iChat. I can do normal chat, but I can not do voice chat with my other friends who have a Gmail account or are using Google Talk. So, how can I configure my iChat to do voice chat with them?
You need iChat as a client on both ends. After this it will be automatically available.
You need Google's voice and video chat plugin http://www.google.com/chat/video
Then you should be able to voice (or video) chat with your Gchat friends