I just finished wrapping the IParticleSystemSceneNode and created an example. I'll send the source code to Nico - perhaps he can use it.
But now enjoy my example:
http://www.the-kotti.de/Demo.zip
[EDIT:]
I added the IMeshManipulator, which improves the room with the MakePlanarTextureMapping-Function. Most of the other MeshManipulator-Functions are wrapped, but some of them need the IMeshBuffer. I'll have a look at it tomorrow.
To get access to the new functions just use the Irrlicht.Net.Dll and the Irrlicht.Dll. They can be found in the zip folder.