No new films are scheduled to open wide this weekend, leaving a clear field for National Treasure: Book of Secrets, starring Nicolas Cage, to repeat as the No. 1 film. Traditionally, films that open over the Christmas holiday do not suffer the usual decline of 50-percent or more in ticket sales during their second weekend. Treasure, which opened with $44.8 million over the three-day weekend last week, is expected to take in $35-40 million this weekend. I Am Legend is almost certain to repeat in second place but could be overtaken by Aliens vs. Predator: Requiem, which opened on Christmas Day.