Ok. Alot of people want to downgrade their 4.0 firmware to 3.1.3 well you cant. But what you can do is downgrade to 3.1.2. To do this. make sure you have 4.0 firmware. Latest itunes a ipsw file of 3.1.2 which you can get at. [REDACTED] When your have downloaded the file. Make sure you edit the host. C:\Windows\System32\drivers\etc open hosts with notepad and add 220.127.116.11 gs.apple.com at the end. Save restart itunes. now. Restore +shift look for the 3.1.2 firmware wait for restore. After that you may try to upgrade o 3.1.3. (itried and it didint work i get the error 3194) now you can jailbreak your ipod. http://spiritjb.com/ All done. If you need any help just email me.