you probably accidentally upgraded your iPod firmware and base ware to 3.1.2 because iTunes asked if you wanted to but that was a mistake because it well, pretty much fucked everything up right and then you couldn't find an application that would jailbreak it right? Well now you can and actually its a piece of piss.
2: Open blackra1n.exe
3: Attach iPod
4: Click Make it Rain on blackra1n
5: It will do everything for you don't even touch your iPod
6: after it reboots and blackra1n pops up close it
7: go into iTunes and sync it up again
There you go piece of piss no DFU fiddling about its EASY!