The closest you can come to developing on Windows is by using a third party framework that lets you build the bulk of the application on Windows, and then doing a final build on your Mac.
This is what I've done via Unity3D and MonoTouch. I do the bulk of my development and testing on a Windows PC, and the iOS specific bits and testing are done on a Mac and on various devices.
I'm not familiar with Flash Builder explicitly but I suspect it's much the same story.