CNC on the cheap

Greetings. I've just joined the group and have an idea that I'd like
to get out there.
I've gotten hold of an old dot-matrix printer that still works (From
Digital Corp.) As is my usual practice, I took it apart to see what's
going on inside, then it occured to me that there is everything there
that's in a "real" CNC: X and Y axes,and another siginal that could be
tapped off to function as a Z axis.
I know (mechanicaly) that I could fashion an itty-biddy XYZ device as
a test bed to learn with as I save for a REAL CNC.
Obviously, I know this would have virtualy ZERO "oomph", Mostly it
would be a platform for learning basic control of a machine. Maybe It
would have enough juice to cut foam or (at best) balsa.
It is the programing/control of the thing that's a mistery to me. I
know the thing works as a printer, 'cause I hooked it up (both before
and after dis-assembly) and it works. It's just a matter of figuring
out how to talk to it.
Any ideas on this?? I'd love to hear what you-all have to say!
Thanks,
Richard