But do they also appear in the movie? Or do they talk about them?
The novel is a spin-off of The Godfather (set during Michael's exile in Sicily), however all references to the Corleones are omitted from the film.
Since you are recomending I suppose it is worth the watch after the book...
Be sure to watch the uncut version. From what I read many reviewers stated it was more powerful, and the uncut one didn't make any sense(Ala Once Upon A Time In America)
Originally released at 115 minutes in the USA. A 146-minutes director's cut is available on Video/DVD
How accurate is the movie in regards to the novel? Has it fallen victim to Americanization?