To make the curves into tube geometry, you have to extrude along their path using the circle as a base shape (if you wanted to create a square tube you could create a NURBS square instead). To do this, first select the “NURBS circle” then SHIFT select the CV curve. Now click (surfaces>extrude>options) a box should appear giving you the following options (Figure: 3) select (Tube/At Path/Component/Profile Normal) and choose Polygons or Nurbs.
Figure 3
This will create a tube along the CV curves, note the NURBS circle can still be scaled and the tubes will resize accordingly, also the CV curve can be tweaked if you wish. When you are happy with the result, you can delete history on the tubes (Edit>Delete By Type>History).However doing so will mean no further tweaking can be done, but frees up memory. (Figure 4)
XVLTR - Final Illustration
Figure 4
This technique can be applied to any geometry -in my case a character- to create a frame. After the long process of doing this on the whole character, I added extra geometry using standard polygon modeling techniques to create more detail, occasionally using booleans to cut holes into the geometry (polygons>booleans) to create sections (figure 5 -> Next Page)