Fourth time will be the charm for 'Shrek Forever After.' The final (we think) installment in the 'Shrek' saga will easily dominate the box office when it opens this weekend. But estimates of how much the green ogre will gross have been all over the map, and the uncertainty has reverberated from Hollywood all the way to Wall Street.On paper, the fourth 'Shrek' looks like an easy winner. The first three were all monster hits, with the most recent, 2007's 'Shrek the Third,' opening with $121.6 million on this same weekend three years ago, setting an all-time record for an animated feature's three-day debut. The new chapter will enjoy a massive 4,359-screen opening, with a record 2,373 of them showing the film in 3-D and 194 showings on IMAX screens, also a record. The surcharges for those 3-D and IMAX screenings offer the film a huge bonus its predecessors lacked. And with fellow DreamWorks toon 'How to Train Your Dragon' finally fading, 'Shrek' will be the weekend's top family draw.
