I got a Precise/Rockwell high speed spindle on eBay a while ago. It runs on 2-phase 165 V power at 950 Hz. It ocurred to me recently that a Gecko 201 stepper driver can output 90 degree 2-phase sine waves at frequencies that high. I finally got around to trying it, and it works! Of course, you can't get full power from a Gecko, but it does allow you to test the motor. I guess you actually could run the motor at about half speed and get full torque. Anyway, it was strong enough to burn my fingers a bit when I put some drag on the spindle.
One warning - if the spindle motor has burned out, it will fry the Gecko drive. I had already tested my motor and was pretty sure it was OK.
Jon