I'm working on a car game too, Automanic (http://automanic.sf.net
). I guess you discovered making a car game gets pretty tricky.
First off, pclinmove and pcmechobject dont mix. The way mechobject works, is that Crystal space sends information to ODE about the positions of objects, ODE does the work in its own physics world, and CS updates the positions of the meshes based on this. So using pcmechobject, you cant move anything by moving the meshes, you have to work on their mechobjects or rigidbodies. Linmove and its collision system works by moving the meshes around. The other thing is that it will be nearly impossible for you to get proper physics with linmove, its only meant for moving people.
About the collision with the ground, I'd advise you to use pcmechsys->GetDynamicSystem()->AttachColliderPlane(). MakeStatic on an object never seems to work for me, the cars sink through the ground like quicksand.
You might want to look at the Automanic source code to see how i hacked up things, although the code is a bit messy. Feel free to use the models if you want, too