If you're planning on making an application with a standard Windows GUI,which I reccomend, you should use C++ or VB. Out of the two, VB would probably be alot faster and easier to code.

C++ is MY main language, so I'd pick C++. If you do pick C++, then you'll also have another choice to make: a Development Environment to use. The two obvious big ones for writing Windows GUI apps are MS Visual C++, and Borland C++ builder. I have no experience with Borland C++ Builder, but I can tell you about Visual C++ (if you are familiar with it then disregard the next litte bit)...

Since C++ has no GUI with the actual language itself (and most languages don't), Micro$oft provides what is called MFC (Microsoft Foundation Classes), which is what you'll have to be working with. MFC is HUGE, however, you won't have to learn it all entirely. You can probably get away with pointing, clicking and using the Class Wizard in Visual C++ to get some of the program's functionality happening.

If you don't already know VC++/MFC, then I suggest that you should at least have a strong background in C++ before even trying to learn it (unless you are happy with what the class wizard builds for you, which is usually not the case). I, myself, have just started learning MFC this autumn, so I couldn't recommend any good books on it.

Oh yeah, another thing you may want to check out is wxWindows. You can write apps with the standard Windows look using MFC (or GTK+, Motif/Lesstif if on UNIX) inderectly. It's open source, and it's portable. :) There's an IDE for it, too, but I'm not sure if the IDE is good for Rapid Application Development, or if it is for free.

Update:Almost forgot to mention: wxWindows isn't only for C++, it also has bindings in Perl, and other languages. So you might want to consider wxWindows, then decide which language to do it in.