Step Motor is not very good for Animation Laser.

It suit for beam laser light Show.

After some searching i have found out some info on using steppers that make me wonder about how would i go about using them.
1. get the largest step possible.
2. the most steps per second.
3. put constant current on one of the coils to act as an electronic spring.
4. Use a varying ac audio amp to power the other coils.
when using the amp make sure the power is set just high enough not to break away from the holding coil.

I have found a motor with a 7.5 deg of step thus i could get around 14 deg of motion easily. (don't want to break away from holding coil so leave the .5 as a buffer.)
It might seem that using a cnc controller is over kill but i could use a cpu 5.1 surround sound card. but what controller to use.

What mods would i have to do to the card to get it to output enough power to turn the motor?
Any software use sound?

If you're going that route, you'll need an external amplifier like a stereo or dedicated audio amp. No current software (except some really old one I think for macintosh computers) use this type of output system. Even then all you're going to be able to draw is some scribbles or lissajous figures.

Commerical stepper units actually step the motors with a stepper motor driver, and a controller to send the step/direction signals. You can make basic shapes and some text this way. Otherwise you really should be looking into some commercial scanners.

My first scanner was built as you describe using steppers. But, I used a microcontroller instead of a sound card. It was a fun project but pretty worthless for anything but very very very basic shapes (ie a square or a line)

So it still seems using my micro controller from my cnc machine will be the best way to drive them. Now i just need to find the motor with the most steps per second.
How many steps or equivalent does a sp20 go?
if i could get a step per second of 1000 that would be over kill for a beam show but maybe just enough to write letters?
i know i am not going to get any where near the results of a sp20 but i just would like a benchmark.

You also want to get the one with the most steps per revolution. This will increase your resolution for drawing images.
There is no "step equivalent" for the SP20, they are completely analog.

I used stepper motors with large steps and only varied between one step. It was easy to make it work that way.