Thanks for the xxcopy link - just what I was looking for.
I've just tried to set up a mirror array on a gigabyte mb with the same promise controller and failed. Failed initially using the existing disk (think I mirrored the new disc onto the old one!) then reinstalled XP onto the 2 fresh drives - once I'd figured out how to load the raid drivers as there was not a floppy with the mb. The array worked, as in both drives had identical data, but XP was very slow and crashed frequently and eventually terminally. So I've gone back to a single drive with the other being for an identical backup.
Incidentally, the promise book says to have a separate lead for each of the mirror disks.