Pff, pues para no explicarte todo te pego esto de Lasse V. Karlsen:
Citar
You can not make kernel-mode device drivers in C# as the runtime can't be safely loaded into ring0 and operate as expected.
Additionally, C# doesn't create binaries suitable for loading as device drivers, particularly regarding entry points that drivers need to expose. The dependency on the runtime to jump in and analyze and JIT the binary during loading prohibits the direct access the driver subsystem needs to load the binary.
There is work underway, however, to lift some device drivers into user mode, you can see an interview here with Peter Wieland of the UDMF (User Mode Driver Framework) team.
User-mode drivers would be much more suited for managed work, but you'll have to google a bit to find out if C# and .NET will be directly supported. All I know is that kernel level drivers are not doable in only C#.
You can, however, probably make a C/C++ driver, and a C# service (or similar) and have the driver talk to the managed code, if you absolutely have to write a lot of code in C#.