What you need in the Spline Modeler is cross-sections. As the tutorial says, the best way of getting these is to do them in Illustrator and import them - not very helpful if you haven't got Illustrator (but they are on the CD). Drawing them in the SM is not easy as, as you say, there's no way of tracing. It is possible to see what you are doing in the Preview window though, and you can drag this to enlarge it, move stuff around etc., all from within the SM (But to see the plans make sure the Textured render button is clicked like in the Assembly Room).