You need to use an older version of iTunes (8, I think, google for it) and DFU mode. No matter what I tried, the 2.2.1 FW would not stick, in the end I flashed 1.1.4 (from 3.1.3) where it got stuck in the middle of the process. From there, I flashed 2.2.1, and it worked
Now, I'm guessing that from there you could downgrade to iTunes 7, and flash 1.1.4.