Any computer will do.
Moi3D has the advantage to work with really old computers too, dual-core and quad-core as well, graphic memory 500 mb+.

So any laptop will do fine.
Recommended is instead to purchase a wide-screen monitor simply because
a 15-17 inch monitor with CAD-work isnt too optimal in many cases a 24 inch widescreen monitor
is of better usage.
Then you can extend the first monitor to the second and use that as a main work area.

But then again, to answer your guestion, any cheap laptop will suffice!

Mvh