Originally Posted by SlyMaelstrom
You need a graphics API... and that's about it. :)
There are several popular ones like wxWidgets and Motif, depending on the platform you're developing for. You can also use Window's native API which is usually available with any compiler distribution for Windows. Your best bet, however, is to buy a book on GUI programming in C++. You can google for them or search Amazon, there are several. Not only will they explain the ins and outs of it, but they'll also likely be teaching a specific API which could be helpful.