I have read a bunch about developing applications for the iPhone recently.  I think that the Safari for Windows is a good start, but it won't solve every problem.  Having developed software for a mobile environment in the past, I can guarantee that the inputs from a PC and from a mobile device are definitely different.  As a result, the entire user experience is different.  Testing on a system with a keyboard, mouse, and a large display will result in a different outcome that someone actually trying to run a web application on a handheld device.  This is a good start, but we need a full emulator that runs on Windows as well as access to a true SDK so that we can write applications that natively target the iPhone.  Sorry Apple, but you still have work to do.