If you look at the bubblejet printer that has the DC motor you took apart to the back of the carriage you will see a plastic strip that looks grey, on careful inspection under a magnafier you will see this grey strip is actually lots of vertical black lines that a laser sensor counts as the carriage moves back and forth, there is also round discs on some shafts the same and i have used many pf these sensors for other applications (like in an anemometer), they are easy to use.
So you can use the old bubblejet with the DC motor and get better positioning than with a stepper motor.
The other method would be to build a cnc machine which i also have done that i use to construct circuit boards and do the drilling of those 100s of tiny holes.
With a cnc machine you would zero the corner of the paper and then set the X&Y coords to where you want the machine to travel to.
The easy way to do this is a premade stepper driver board that will allow for 3 axis, and they are rather cheap off ebay.
I have used several of them now and the plug direct into the parrallel port and work with standard cnc software like Mach3 etc.
As for the lead screws for a small cnc i used allthread as it is cheap and easy to work with.
Pete.