gear indicator (by Kada) might be better use of lpt port... I am using this thingy for about 2 years and everything works just fine... supported features are: low_fuel, shift_light, traction_control, signal_lights, handbrake, rpm_limiter, redline and of course gear number
and it even supports RBR! (win xp only)
it's a fault of drivers. i've had same problem (169.21) and another drivers solved it. now i'm using DNA-Force_4.0.16904x32-[www.guru3d.com] and everything is fine.
you should try the newest beta drivers or some modified ones...