I found the
download page for 5th Gear, installed it and ran it. But I could only get to the main menu because the actual simulator requires PhysX, and I have an AMD card.
Edit: I got a PhysX installer
here, but it seems that you have to have a dedicated server to play.
Edit2: I was able to run a server and a player at the same time on the same computer, but neither would show a field. Not sure what to do from here.