A lot of people have been asking about using the existing open SDK for 2.0 application development. A few betas back, my answer was "Hey, no problem". But with the last two betas, I'm not quite so sure. We haven't seen pwnage compatibility since the third beta and there hasn't been a concerted effort that I've seen to upgrade the open headers to match late frameworks. (I know I haven't documented headers because of NDA concerns. That's probably goes for many other programmers.)

As for using the old headers, that's simply a no-go. Without going into specifics, Apple has definitely evolved its firmware and the underlying frameworks. There's a semi-recent open toolchain available here but until 2.0 is officially released, there's no general way to deploy and test the specifics.

I have no doubt that a 2.0 openSDK will appear at some point, even with Apple's proprietary attitude towards iPhone platform security. That being said, do not expect simple ports from 1.1.4 source and headers. The target has moved. The classes have moved. The paradigm is re-defined.