Why can't you plug it in and find out for yourself? There is this list though.
It worked on GT5, and I'm 99% sure it works on GT6.
In fact, I'd be shocked if it didn't.
The old Driving Force Pro is way better than the Driving Force GT so I don't blame you for hanging onto it.
Once you're ready to upgrade to a G27 or T500 though, you'll realize that the Driving Force wheels are essentially just toys though.
Didn't the original Driving Force have PS2 controller plugs? I know one of the pre-DFP Logitech PS2 wheels did, but I'm not sure if it was that one.