twirl a line... Hmm... let see...
if you mean line as in the draw a line, then I would use nurbs curve lines for curved lines, other then that, when using a straight line... extrude it by zero(using modifiers.) then make it a editable polygon, then select edges(for editing polygon.) then go to the edit edges tab thing (:S).
then select insert vertex, now select a part of the line and put vertexes on it

then go to vertex editing mode, select a vertex one by one and pull it out or in, each one at a diffrent time not all at once

hope you undertsand what I mean by that, rofl, i aint the best at guiding people... xD

No doubt'fully the simon cowell of the fpsc section :S