If you already know C# and a bit of trigonometry, then it should only take you a few hours a day for a week to learn the basics of Managed DirectX 9. I used the free Borland C# Builder, but I suspect that Microsoft Visual Studio (or Visual C# Express) would offer slightly more polished interfaces. C# Builder would sometimes fail to offer help on clicked functions, forcing me to navigate to the relevant help pages manually, and its autocompletion of functions (cf. Intellisense) was not comprehensive.
I found a number of DirectX 8 C++ and DirectX 9 C# tutorials useful. It's not always obvious how the calls change from the former to the later, but at least it shows you what is possible. I recommend following the tutorials listed below in the given order.
- Riemer's DirectX 9 Tutorial (C# DX9). A brief, easy-to-follow tutorial that quickly produces impressive results.
- Drunken Hyena Direct3D Tutorials (C# DX9). Covers pretty much the same areas as the previous tutorial, but explained differently and in more detail, so useful in filling in gaps.
- Craig Andera's DirectX Wiki(C# DX9). Goes much further than the previous tutorials, exploring topics such as materials, textures and lighting in great detail.
- Andy Pike's DirectX 8 Tutorials (C++ DX8). Don't let the C++ put you off. Goes into a lot of detail on a lot of topics.
- Using Managed DirectX to Write a Game (C# DX9). Unlike all of the other tutorials, this actually leads you into producing a playable game. It's not as detailed on theory, but has lots more practical advice.