[JesseK]

To simulate the hardware (e.g. a Gyro) you could have a knob or slider that represents the sensor input. When you hit run in Labview, at the appropriate times you can manually move the knob to simulate the robot's feedback (e.g. move the knob to the gyro's equivilant value of -90 degrees to simulate a left turn). I would then recommend setting up a few graphical outputs that show what the motor outputs are.

It will be hard to fine-tune any PID control with this method, but it should at least be able to expose any errors. I'm going to play with Labview tonight for the first time in a few years, so I'll see if I can give you more details then.