Hi Rainer re: spiral on a sphere - if you can draw a curve that is close to what you want, you can then sweep a line along it to get a kind of ribbon like surface and then intersect that with the sphere to get your final curve.

Check out Danny's post in this previous thread for that kind of method:
http://moi3d.com/forum/index.php?webtag=MOI&msg=3530.1

But it may be kind of difficult to get the path shaped well in the pole areas.

- Michael