Making a surface of a mountain from several contour line

Hi

I want to make a complex surface like a mountain from several contour line.
Some contour line is a border of the mountain surface but others should be the constraints on the surface.
And the tangent and the curvature should be continuous on those contour lines.

I am reading the manuals but I cannot find out how to model the mountain surface.
Does any one help me?

Hidek