What resources to look to in order to write an emulator for iPhoneOS?

What are available resources I should look to in order to write an emulator for iPhoneOS? I'd like to write an em开发者_开发知识库ulator to run applications written for MacOS. I understand that I won't be able to use file system and other OS resources. I do have an SDK, XCode and all documentation for those resources, but I wonder if I can find some examples (perhaps similar to the emulator that can run Ninetendo games on iPhone)?

You might want to look into this: http://www.tuaw.com/2010/04/13/rhapsody-on-an-ipad/. Somebody used a modified version of Bochs to run an older version of Mac OS ("Rhapsody") on an iPad, which runs iPhone OS.

Note: As mentioned in a comment, you won't be able to sell or distribute your emulator via the App Store, and running Mac OS on an iPhone or iPad violates license agreements.