If you had a DF Pro, you didn't have to buy a G25 to have a quality racing wheel for Prologue. I did buy a DF GT wheel because my PC ate my DF Pro, and I did buy a G25 when I learned that it was guaranteed to work with PC games, and knew it would be about the best wheel for GT5.
But if you bought a 360, you couldn't use a wheel which worked just fine on a Playstation console. Unfortunately.
Well you can now i have ordered the Fanatec wheel which works with the 360 and the Ps3 and the PC.
http://www.fanatec.de/webshop/new_eu/product_info.php?cPath=21&products_id=61&session=true