basic USB help

I wanted to see if I could send a basic signal over a USB cable to some custom device to-be built.. let's say a servo motor for now. How possible is it to send data to something like this? I imagine it wouldn't be easy to detect a device with such basic circuitry (digital-to-analog converter... and probably an amplifier). How would I go about doing something like this? I have read a few articles detailing writing USB drivers, and another article showing how to do so from user-space. I'm completely new to the driver arena, though I can program fairly well, so I didn't know how possible it was to communicate with such a custom, lower level device.

Thanks
Eric