"What I'd hope to happen is a big error message "you can't do that
dummy"
and then crash my computer or something."

Just let windows take care of those things for you. g

I agree, Edwin, you should give a couple of them a try. Most CAD
software will have some sort of free trial period if you download off
the net. SketchUp has an 8 hour trial period. That's 8 hours of program
open time.

Take a look at the training videos on their site. They'll let you see
what SketchUp can do.

By the way, one thing that is nice about SketchUp is that you can
ignore dimensions altogether and basically just doodle to get an idea
of what something might look like. Then you can clean up and adjust as
needed to get to a working drawing that you take to the shop.

Think of that as starting out with a big fat crayon, drawing shapes
freehand until you get what you want. Then switching to a sharpened
pencil and a ruler to do a final drawing.

SketchUp has a several functions that make it a wonderful tool for
woodworkers. First, the Push/Pull tool which allows surfaces to be
moved perpendicular to the face. Another is the Rescale tool which will
allow you to adjust the size of things without redrawing. The third
cool tool is called Follow Me. It allows you to draw a profile and then
extrude it along a path. This is useful for drawing moldings as you can
draw the cross section of the molding and then extrude it to follow the
shape of the cabinet or whatever. You could use this function to draw a
picture frame or whatever as well.

Dave