directx - How do I create a decal system?

I'm currently given the task to design & create a simple decal-system in C++/DirectX.

Does anybody know a great tutorial, article or paper to start with? (Especially the part about 2D-texture to 3D-surface projection and clipping isn't entierly obvious to me.)

I'd also appreciate just simple hints and best-practices.

Answer

An example of what you might be looking for:

These forum topics should help you get started:

I am in the middle of writing my decal system (C#, XNA), and it is going pretty well. So let me know if you need some help. Here is a video of it in action: http://www.twitch.tv/battlekiller/b/308505930 . (The decal is the yellow spell circle following the mouse.)