Before the big event, the running of ALMS's New England Grand Prix, which is stop number 4 in the ALMS, there were three different preliminary races - IMSA lites, which are cars like the Radical, which feature up-and-coming starts of sports car races, American GT Challenge, which features modified Corvettes, Camaros, and Mustangs, and F2000, which, near as I can tell, feature open-wheeled cars with small engines.
Here are some American GT Challenge pics:
F2000 pics:
Many more to come...