Is Mac OS X required to submit an app to the iOS App Store? We are about to develop an application using Phonegap, a cross platform mobile development tool, but they offer a service where they will build your applications and send you the compiled source code. 

Can I submit the compiled source code to the App Store on a Windows-based PC?
No, the compiled code must be submitted via a Mac. One "workaround" is to install OS X into a virtual machine on Windows, but that violates the OS X user agreement. So yes, you'll need a Mac.