Mole,
Well, I can't tell you how this is going to work out exactly, but I can say that there will be, ah, wrinkles.
There currently exists two pretty good, ready-made USB-to-gameport adapters, though I think the better one is no longer in production. It even works in Vista, and I've already tested it.
This however, is only part of the equation: this hardware ALSO needs a PS/2 or AT keyboard connection to transmit keystrokes. There do exist USB-to-PS/2 adapters, but the one that I've tried *may* have had something to do with frying my keyboard controller chip in my WCS. Or it just died on its own. In short, until I get a larger supply of replacement parts, I won't be trying *that* again.
There is also the matter of programming the stick. You still need DOS (or Windows 98) to send the programs to the stick. For this you DEFINATELY need a standard keyboard port, and PROBABLY 5 volts power in the gameport, but I'm not sure if the USB gameport adapters will do this under DOS, without a driver.
A Bootable USB drive (or memory card) with DOS and the thrustmaster software will do the job of sending the programming to the stick, and then you can reboot to XP or move the stick and it still works.
There's also the matter of the Digital Stickworks Chips that Bob Chruch made a few years back. They don't need a keyboard connection, but their drivers only work in 98 and XP (and not Vista), AND they apparently don't work with the USB to Gameport adapters. I still need to test this too.
Another solution is to build your own, with the component at:
http://www.lbodnar.dsl.pipex.com/joystick/This should work in Vista, AND will smooth out the spikiness of the thrustmaster pots, BUT you'd have to manaully rewire every button and hat yourself inside the stick, AND you'd lose the programming options. Or you could use it just for the axes of movement and not the buttons.
I'm currently researching all this, experimenting, and starting to write a guide on my website:
http://www.warrenernst.com/ called "The Book of Thrustmaster: Windows Vista and XP Edition."
-Llama