With itunes load fw 3.1.3

Then after do the link (I did it with redsn0w 0.9.4 not with 0.9.2)

iClarified - iPhone - How to Unlock/Jailbreak Your iPhone 2G on OS 3.1.3 Using RedSn0w (Windows)

It' works!

PS: When I try do it directly with FW 3.1.3 redsn0w does not identify the firmware so the process does not begin