The simple answer is: you don't. You don't uninstall it. You restore it, and that is the only way, that I know of anyway. When you download the 1.1.1, save it. That way if and when you want to "uninstall" it, you simply plug it up to your computer with iTunes open, hold the top on/off button and the home button down until the screen goes black with a few dark bars across it, then you let go of the top button while continuing to hold down the home button; you can let go of the home button when iTunes brings up a message saying that it found an iPod in recovery mode. Then you on a PC you hit Shift-A (on a Mac it's Command-A I believe) and click restore; then you can select your 1.1.1 file, and let it do it's thing, and then you can update, or you can just click restore, and it will download 1.1.2 (or the latest update) automatically. Personally, I would put 1.1.1 on first, just in case it would make a difference in the jailbreak being discovered by Apple in the case a repair being necessary. But that it the way to "uninstall" a jailbreak.
