Hi,
Just compare the value you get from the ADC with the value that corresponds to 2V, if higher then run the motor, if lower then stop it, you can figure that out. You may need to introduce some hysteresis around the threshold.

Then send the value to the PC using the PBP's SEROUT command, or even better use the USART, a MAX232 level shifter and the HSEROUT command, see the manual. There's many examples on the forum.

For the PC/VB side have a look here: http://www.rentron.com/VisualBasic.htm
Just send the raw value from the PIC and use VB to scale it to volts if you like.

/Henrik Olsson.