It sounds like you may be looking for the bone transforms, which define transforms for each mesh in a model relative to the model's coordinate system. This lets you, say, rotate a car wheel about its own axis, and keep it correctly positioned relative to the car chassis.
Assuming that you have already loaded a model with
var model = Content.Load<Model>(@"mymodel")
You can easily get to the bone transforms with
See this link for a decent explanation, or this one from Riemer's.
This XNA App Hub sample demonstrates loading a tank model, and having its wheels and turret move relative to the model.
The basic idea is that different meshes (in this case, the wheels and tank) are connected via "bones." Bones represent a hierarchical relationship between model elements (despite the name, they are not exclusive to animal or human models).
In your 3D modeling app of choice, you define bones connecting child meshes (wheels) to parent meshes (the tank chassis), and define transforms in the child mesh's space that transform the mesh relative to its parent.
By using the
.CopyAbsoluteBoneTransforms() method, you can quickly concatenate the child's transforms with the parent. This has the effect of putting the child mesh in the parent's coordinate space, so that you'll get a valid result when you multiply the result by the view and projection matrices.