.Net (dotNet) wrappers for OpenCV?
I started out with opencvdotnet but it's not really actively developed any more. Further, support for the feature I needed (facedetection) was patchy. I'm using EmguCV now: It wraps a much greater part of the API and the guy behind it is very responsive to suggestions and requests. The code is a joy to look at and is known to work on Mono.
I've wrote up a quick getting-started guide on my blog.
We use OpenCVSharp the google code website is in Japanese but it uses the latest OpenCV builds and impliments IDisposable throughout. It seems to provide more functioanlity than any of the others we have seen to date and is still active. It has quite extensive example programs as well.
I think it's important to note that the original question was asked in 2008, and OpenCV 2.0 was released in 2009. The version 2.0 release introduced a C++ wrapper which is significantly easier to work with than the older C interface that the OP was confronted with. For my .NET project, I'm leaving all the graphic manipulation in native C++.
Try this: create a C++/CLR DLL project which links to the OpenCV libraries. The OpenCV manual describes how to do this for a Windows C++ EXE, the same steps also work for a C++/CLR DLL. Then of course the DLL exports methods which are callable from a .NET EXE.
To test it, you should be able to incorporate any of the OpenCV samples into your DLL with a little tweaking. (Add the .CPP file to your project, convert the main() function to a class member, etc. - you know the drill...) A good test candidate might be the "mat_mask_operations" sample.