Here's a little gadget I made for playing around with Bezier curves. Curves with three points are the type Flash uses, curves with four points are used by Illustrator and other drawing programs. Curves with more than four points are rarely used because the amount of computation required increases exponentially with the number of points.
Drag the control points to manipulate the curve.
If the curves appear too rough, increase the detail level. If the program is running too slowly, reduce the detail level or the number of points.