It is my understanding that if you are a Ferrari owner, you can schedule a Factory tour through you local dealership in advance. If you are a non-owner, or not part of a previously scheduled organized group tour (for example with a Ferrari club), then joe public is only allowed in the reception room. I visited in 1992, and the reception area usually has a couple of important cars on display as well as an F1 engine. But there is still plenty of Ferrari stuff to see within walking distance of the factory...Galleria Ferrari (excellent museum); the factory store; several other memorabilia stores; and the Cavallino restaurant. See the recent pics posted in the Photo Gallery section from a fellow Ferrari-Talker about his recent visit. Have a great time.
I was in Maranello on June 11. Before my trip I checked with my local dealership to register for a factory tour and I was informed that the factory was going to be closed for visitors until further notice, perhaps September or October.
They do that when they are working on new projects (ie.: the 360 replacement).
However, as Paul says, there is plenty to see, all Ferrari related.
There is now a Hotel across the street of the Factory called The Red Planet Hotel, there is also a restaurant/bar called Red Planet Cafe (although I prefer the food at the Cavallino Restaurant).
From Modena just take Via Emilia Nord and it will take you to Maranello.