Mach doesnt write to the registry as far as I am aware so the onl;y remnants in the registry will be Windows own tracking of Mach. To uninstall Mach all you do is delete the directory.
Hood

To get back to the rest of your post - yes, the motors will probably be 200 steps per rev. I would use the drives set to 10 microsteps - which will give 2000 steps per rev.

You seem to be saying that the thread pitch is 18 teeth per inch. This seems an odd figure. My old Acme was 10 revs per inch, my new ball screws are, of course metric at 5mm per rev.

If your pitch is 18 per inch, then your steps per inch work out at 36000. Should be OK for some nice accurate work.

Thanks Jim, got my CNC working this weekend, on the new and the old version of Mach 3, just wanted to make sure that it works on all versions, including an air cut, which work flawlessly, I love this hobby, can't wait to cut some interesting patterns, next is getting some cutting bits for my router.

I am thinking of remaking this same setup but with 4 axis or with the gantry that will rotate 180 degrees, Hobby CNC 4 axis Pro board and a table that could be tilted which would allow me to cut 360 degrees, I have an idea we shell see if it is doable.