How could I enable the 'Shift' key to be able to generate a curve from the

Maybe you have seen this:
http://tavmjong.free.fr/INKSCAPE/MANUAL ... ths-Bezier

"To begin to draw a curve, click-drag on the canvas. The point where you click becomes the end point or node of the curve. As you drag the cursor, you'll see a gray line between the end point and the cursor. This line is a tangent to your curve at the end point. "

Not really what I am talking about, once the vector is drawn. I want to click the (straight) path and drag it to generate a curve.

Anyway it seems I no longer need to press SHIFT for 'grabbing' the path and now is done automatically. And wasn't actually with the pen tool but with the Node tool