First off I have an Xbox as well, from what I can see only Fantech do one that works for both. I of course own both consoles, and love Forza as well. I cannot justify forking out for a wheel that only work on one.
Bite the bullet. Get very patient. Get a Fanatec GT2 CS. Patience patience... When you get it, you will never, EVER, look back. I got angry waiting for it, I regreted paying 500$ , that is, until I got it.
Man this thing is like touching breasts for the first time...
You obviously did not go to the link in my post. It's a converter for 80 bucks that allows it to work, just like the fanatec. It's the best option for G27 owners who may be looking to pick up Forza 4 if GT5 doesn't clean up its act by then.