I would update via iTunes to iOS 4.2.1 and then run Greenpois0n. x98's answer is correct, but it can be a pain to find the correct version of greenpois0n for 4.1.
If you go to 4.2.1 limera1n won't work, but greenpoison will.
Still dont know what you mean by limera1n restore ipsw. Limera1n is a program, it doesnt require a .ipsw. You must be talking about a custom firmware made with pwnage tool or snowbreeze.