Owen,
To add to Mark's comments, I suggest you also look at the Rasterex Graphics
board. It works much like CAD Overlay, but their software runs directly on
their graphics board. Very fast. They are about to introduce a new
software product that allows "intellegent object picking", speeding the
conversion process. Hot product.
Also, consider useing a local scanning service to provide the scanned
images.
Ken Elliott /// CAD Masters