Is it possible at all? Some apps on iPhone are iPad are quite nice that if it can be run on the PC or a Mac it'd be nice.
3 Answers
The iPhone SDK provides a simulator, but I guess that it requires you to have the source of the application you want to run. You couldn't run any binaries taken from the web.
For more info on the official dev kit: http://developer.apple.com/iphone
The iPhone and iPad use ARM, PCs and Macs use x86. Without an emulator or a port you cannot run those apps at all.
It actually is possible, but requires the author of the application to bundle the App specifically for you to use in the iPhone Simulator. (You'd need to have the iPhone SDK installed as well, which requires an ADC membership.) I doubt you'd get authors to bundle their apps for use with the simulator for non-beta-testing or screencasting purposes. See Simulator Exchange for more info.