assuming a 8" rise, and a 10" run, and 1" plywood for steps:
All you have to do is build a 1x4 frame for each step. example. Step number 2 is 16" from the ground. So build a frame that is 15" tall. Then all you have to do is nail another piece of 1x4 to the front of it, at the height of the previous step (minus the plywood). this board would be at 7".
See the pic...
staris.jpg
This setup is great because it can collapse and be stored for future use, and because each frame is independent of the others, they can be aligned in any curve and a step can be cut to fit. Naturally braces will have to be added for additional support and rigidity