Mark Biasotti has done some nice tutorials on splines. One of them covers exactly what you are trying to do. I believe it is the one called "Working with Splines":
Thank you for the tip about the Mark Biasotti tutorials. They are very very good for a spline and surfaces newbie like myself. I watched the Working with Splines one and I am now working my way through the Everything Curves and Surfaces. Excellent.