usually to draw a model you need to setup its vertexbuffer, its indexbuffer and its effect.

So the first draw will need a setup... and the second call another setup... that replaces the vertex buffer, the index buffer and the effect, but not destroy them, the continue living in gpu memory.

Don't use DrawUserIndexedPrimitive... create an individual vertexbuffer for your moving objects.. or group all your moving objects in a vertex buffer to share it...

in your object draw call, you can set an individual indexbuffer and transform the position passing the world matrix to the effect