So I joined the Apple development program (cost me $99) and downloaded the Beta 3 version of iOS 4.1 for my iPhone 3GS. When I loaded it on the phone, it would not activate. Oh crap, iTunes goes out to the web and checks to see if your iPhone has been registered as a development platform and I hadn't done that. OK so into the Apple development site to register my phone. Now it want's to know the phones UIDD - how do I get that? According to the documentation you get that from iTunes after you plug the phone it, but you cannot do that when the iPhone is bricked! Solution - Configure Windows to display hidden files & folders then navigate to c:\users\all users\apple\lockdown and you will see a file like this:
The number (without the .plist) is your UIDD. When you enter this into the registration page and wait for a few minutes before restarting iTunes, your phone will activate. Phew!