How to Jailbreak the iPhone 2G
1. Review your firmware version by going to Settings> General> About and check your Version
2. If it is 3.1.3, simply download the firmware but do not update and continue to step 3, if it is lower press "Download Now" and follow the instructions in the video down below on how to safely update your iPhone. Once you have updated your firmware, continue to the next step.
Here are the rest of the firmware links for this device if you wish to use them. (experienced users only)
3. Download redsn0w for your operating system.
4. Follow the instructions in the video below to jailbreak your iPhone (for both Windows and Mac). The guide is meant for ios 5.x but it works with your device too.