You can assign textures using the world editor, simply select your car and go into the material editor. Alternatively you could manually do it by editing the material.cs file
I learned and I bet you can too. Use blender. Wouldn't be hard to model what you did here. And it wouldn't break the groups and everything else up. I learnt to stay away from sketch up for vehicles. So give that a try.
I REALLY need to learn/get used to using blender or max soon, but I will not try to model anything more at the moment in SketchUp, or else I will just dig myself in deeper.
I don't think that'll accomplish anything besides depriving us of your great mods. There will always be people stealing this stuff.
This is what I was planning to do with my 450r. JDMClark under a fender or somewhere modeled not texture so it can't be covered up that easily.