[Rickertsen2]

by force feedback do you mean something that vibrates or something that actually resists your movement. I have thought it might be kind of neat to use either style of feedback to communicate how much current the motors are drawing. An accelerometer could work too. I I definately think its a worthwile endevour.
The only ways to communicate back to the OI are through the dashboard port and the LED outputs.

Reading the data off of the dashboard port isn't hard but you need a microcontroller for it.

The other approach is to use the LED outputs. By themselves, these can't source enuogh current to drive a vibrating motor, but you can easily build and amplifier for them.

Now this brings us to the issue of where to get power. Its not available in a great enough quantity from the OI, so you will need an external power source. A battery will do.

As far as the legality of this goes i don't know for sure but i can't think of any rules off the top of my head that it violates. It seems to me that a vibrating motor is the tactile equivalent of and LED.

There are some people somehwere on this forum that built a playstation controller->gameport adapter. I am waiting for them to release the source for this. Once they do, it would be pretty nifty to add force feedback support.