Q:

iPad/iPhone app developement in C++ on Windows OS

What is the fastest way to port an finished game project written in C++ to iPad. Is there any good way to do it without buying a Mac?

A:

Marmalade (formerly Airplay SDK) is a cross-platform SDK that is well-suited to games. You can write your code in Visual C++ and run it in Windows in a simulator. Using a PC, you will not be able to debug (stepping, breakpoints, etc) your game while running on an iPhone. Deploying to an iPhone for testing (from Windows) seems rather tedious, compared to how it's done with XCode.
If you need to use iOS native API features that are not supported in Marmalade, you can build wrappers to them with the EDK (Extension Development Kit), but you'll need a Mac with XCode to build the wrapper library once.
If you decide to get a Mac for development, the cheapest route is probably a Mac Mini and a KVM switch that will let you use your existing keyboard, monitor, and mouse. It's cheaper to upgrade the Mac Mini's memory yourself than to buy a Mac Mini with more memory pre-installed. You can order Mac memory upgrades from online computer retailers cheaper than from the Apple store.
See also:

Marmalade Mobile App Development - Is Marmalade a Good Choice?
Is Marmalade SDK more relevant or commonly used for Game Development?
Native Android/iOS development vs Marmalade SDK

ADDENDUM
I forgot to mention that iOS already has native support for OpenGL ES, and that XCode can compile C++ code. It's also possible to mix Objective-C with C++. So you can keep your C++ engine more or less intact, and write wrappers around iOS-specific facilities, such as detecting user touches.

