To make a pipe, you could use Object->revolve (revolve an ellipse). or you could use the Tools->replicator to extrude a shape.
Something which is fun to try with AC3D 4 is to use subdivision to create 'bendy' pipes. e.g.
This is a rectangle that was extruded a few times, then the subdivision level was set to 2, from Tools->object-property-editor.
To change the diameter - resize one of the 'sections' of vertices.
Sorry, I'm not sure what you mean about making the track.
Andy