go to iClarified - Apple News and Tutorials tutorials, iPhone, Jailbreak and look for the iPhone 3G. Pick your firmware and pick your method, I believe the 3G only goes as far as 4.2.1 but really if you ask me 3.1.3 was the last firmware worth using on the 3G. The links to the tools might be dead in the tutorial because that is older stuff but you can yahoo them and find them on the web somewhere.