Tobias Oetiker graciously released some patches I submitted that allow users to build the excellent RRDTool library with Visual Studio 2008 and up. I updated Stefan Ludewig's instructions with links to the latest dependencies and updated the solution to make building a little easier. All of the traditional RRDTool functions are working but please note that the daemon and client functions do not work for Windows. You can also build rrdlib to link into your own Windows programs.
While I was at it, I created a quick DotNet wrapper in C# that you can find in the bindings directory. It uses simple platform invoking of the rrdlib.dll so it's quick but there may be problems if you try using it under Mono. I'd like to hear from anyone giving it a shot though. A test application is included with the source.