XY -dc motor control , PLEASE HELP !!

I have two DC motors on my x and y axis with a modified GENIUS mouse
for an encoder.I use QBASIC and my parallel port.

I also use pulse width modulation for speed control.
To cut strait lines 90 and 180 degrees works fine .

Problem 1:
How do I control two DC motors simultaniously to cut a SMOOTH straight
angled lines (other than 90 and 180 degrees.)

Problem 2:
How can I use digital output from my parallel port to the external
pulse width modulator for speed control. (most PWM circuits works on
a var. resistance pot input for control)