I'd say the distinction refers loosely to how much rubber the frame can clear. Greater thn 48mm or so and it's a 29er. My cyclocross bike isn't a 29er, and my friend's Specialized Transition TT bike definately isn't, but my Redline d660 is for sure.
The tires are 622-42. Fairly wide by normal 700c road standards, I guess. I like them a lot. At about 50 psi, they provide a pretty soft ride.