After Sn0wbreeze V1.6.2 has been released, and it came with fixes for Youtube issues and Itunes restore errors, Still some people getting errors while Restoring! they still can't restore using custom firmwares created by PwnageTool or Sn0wbreeze. So here's a new trick or a new way to jailbreak iOS 4 on iPhone 3GS but must be Jailbroken on 3.1.3 with Spirit Using Spirit2Pwn.
Note: If you haven't jailbreak yet, then you can Jailbreak your 3.1.3 using Spirit by the guide posted here. If you are already on iOS 4 (not Jailbroken) then you can downgrade back to 3.1.3 then Jailbreak using the same guide.

Steps: