How to go from 2.5 D to real 3 D ??

Hi All

I am getting closer to running my 3 stepper motors for the first
time, using Dan Mauch's 5 amp boards. Setting aside all the fine
tuning etc, for the moment, I am most curious about cutting metal in
real 3D using 3 steppers, or even a 4th axis (rotary table).

I think I get the concept about what's 2.5 D and what's 3D. In 2.5 D,
you do some x-y movements, then stop, lift the tool in the z axis,
then stop, and do more x-y cutting. In 3D, all three axes can move at
once. Or 4, if you have a rotary device.

But how do you make the jump up to 3D? Right now, I can draw
something in Corel Draw, save as a DXF file, convert to G-code, and
away I go. My drawings are 2-D. I would REALLY prefer to stay with
Corel Draw if I can (instead of AutoCad) but I'd like to try 3D. Do I
have to draw differently, essentially a 3D drawing? Does anyone know
if this can be done in Corel Draw?

I am planning on buying Art's Master5, since I hate DOS, and it seems
to operate smoothly, according to feedback about the software.

Also, how does the G-code get generated for a real 3D operation? Are
the files typically huge compared to 2D work?

Lots of questions, I know, but I figured I'd better get into it if
I'm ever going to see 3 or 4 stepper motors working at the same time.

Thanks to anyone who tries to explain. Tom Kay, Ottawa.