on mine (1G, 16GB) i had 3.1.3 and i just jailbroke it. I saw a video on youtube that you use redsn0w 0.9.2, and then use the 3.1.2 firmware to patch it through. Somehow, it used the 3.1.2 to jailbreak 3.1.3, and now I am more than happy with my end result. Remember not to use Recovery Mode when doing it tough (redsn0w will tell you exactly how to do everything)