I'm trying to compose a hedgehog - the modeling is partly done, and I assigned three materials to the object, two of which have a number of vertices assigned.

Now, when I set up a particle system for one of these materials I was hoping that this particle system (hair) would be restricted to the vertices that were assigned to the underlying material (as would be the case for textures), but it doesn't. The hair grows over the entire object.

I found an example where it is done using vertex groups, but I can't find how to set up a vertex group (neither in the Blender help files nor in the Blender for dummies). Both sources talk about how to use the vertex groups, but not how to set one up.