From what I understand, they have recreated some of the sets. Some of it was filmed in the actual cul-de-sac (a real life cul-de-sac) in Southern California. The reunion will feature a number of the actors who played the most popular characters, including Joan Van Ark, Michelle Lee, Nicollette Sheridan, Ted Shackelford and Donna Mills. They are going to talk about the show and watch old clips. It isn't a new 'show' per se. It is supposedly set up similar to the recent Dallas Reunion which was also produced by Henry Winkler.
Here is a link to the CBS webpage. Makes me mad they didn't advertise this more...
http://www.cbs.com/specials/knots_landing/