I thought I'd put it here also for everybody to find and to avoid that
someone starts another one from scratch :
I've started a .NET wrapper for Newton with The unProfessional.
Actually there are enough functions implemented to make some cool demos.
http://sourceforge.net/projects/newton-dotnet/
There are enough functions to implement new ones without much pain (the hard points are already sorted out).
Look in the cvs for all the .h necessary to create the .NET c++ class project.
If you need some help to use it (it's not out of the box yet) ask here.
If you want to implement missing functions, tell here also.
If you use it to make something cool you can tell here also that would be nice.