A few people have used the Arduino to make laser harps. Search the forum for "harp".

I haven't tried this one but it looks promising and it's free. I think it uses SPI.
http://www.photonlexicon.com/forums/...highlight=harp

This guy sells complete plans for an Arduino based laser for $20. The quality of the documentation is great. http://www.stephenhobley.com/build/lh_arduino.html. I bought the plans when I was first looking into all this but later decided to go with a soundcard DAC. The soundcard DAC system is as cheap as the Arduino based system and there is a ton of existing laser show software you can use with it.

I've had some experience using the Arudino's native SPI interface for high speed communications. You can get about 29k bytes per second out of the SPI interface. I'm not sure how the SPI interface on your DACs will work but say you need to push 4 bytes out for each scan position, that's only 7.25k scan positions per second.

I decided to go with a $215 Scan30LSP from Dave and have been very happy with it. They also have a 20k version for $145.

Mike