My first thought is that your video card isn't up to the task. What are you running?
This is more of a guess than an answer, when rendering with app's like autocad, to be more efficient (ie. faster) they can bypass the usual rendering api and pass it on to a more native (to the video card that is) rendering api such as OpenGL or DirectX.
It all depends on how the graphic primitives are sent to the api also, most CADD programs are not designed with rendering as a first priority, they are more interactive, that's why it's a lot faster to work in wireframe than a shaded mode. Rendering takes it another step again and uses many more resources.
Ask a friend with a good set up if they can render it for you and see how it goes, others with more experience may have a few tips/clues in how to optimise your rendering also.
Welcome aboard!
cheers,
Mick.