Don,
I used CorelDraw for about fifteen years before I ever heard of SU, and I could pretty much do what I needed to do without even thinking about it. Now when I run Corel I have to fumble around trying to remember how it works, and I become annoyed with it for not behaving sensibly like SU.
To use coordinates for the target (to) location of a Move, first start to move the object as normal with the mouse. Be sure to grab the object with the mouse on the point that is to be sent to elevation 0. Once you’ve begun the move, notice that the prompt “Length” appears next to the measurement box and the actual distance moved so far with the mouse starts rolling in the box itself. The rolling numbers mean that SU is ready to receive numeric input, should you wish to enter exact values. As soon as you see these rolling numbers, take your hand off the mouse without clicking and start typing: whatever you type will replace the rolling value in the box. Don’t click in the box. Type a value and hit Enter.
At this point you can enter a length or a coordinate. <x,y,z> (angle brackets) denotes a relative coordinate, and [x,y,z] (square brackets) denotes an absolute coodinate. To send the object to the ground, leaving its x,y coordinates unchanged, use absolute coordinates and omit values for x and y, using only comma delimiters to mark their places, thus: [,0].
-Gully