1. How can we create an ipsw file for the iPhone that can later be used to restore the firmware.

2. Is it possible to restore iPhone 2.1 ipsw file to a 2.2 device; will the device downgrade to firmware 2.1.

1> Pwnage Tool
2> Yes you can but you may get an error when itunes tries to downgrade the baseband (the error is because it cannot do it) in which case you will have to kick the phone out of recovery mode with a program like iliberty (I think quickpwn gives instructions to do this if you plug in your phone and try to quickpwn it when it is in recovery mode).