3d problem

trevor,
as long as the cross section of pipe in question does not change at any time during the curve simple use the torus entity. match the radii, and, essentially, align the two shapes with tangent snapping, this will enable smooth and flawes transistions.
i don't know how much you know about 3d, but the last time i did that (3 years ago) it requires extensive use of modifying the UCS coords for a particular task [one of the major set backs in modeling with autocad]
hope this helps. post again if need more ass!
rockon remember, its not work, its autocad!
adam

You can extrude a circle, using the pipe centerline as the path.