With the weekend's No. 1 film doing only lackluster business, not much more can be said for the rest of the crop. The horror film "People Under the Stairs," from director Wes Craven ("Nightmare on Elm Street"), opened in first place, but its numbers don't bode well--especially for a movie in this genre, which typically has one opening burst of business. Grosses took a 38% plunge for the hip hop comedy "House Party 2," falling from first place a week ago. But second place "Curly Sue" countered the trend, with business jumping 7% in its second week. Among openers: "Highlander 2--The Quickening" came in third, with the highest per-screen average of the week; a tepid "Billy Bathgate," opened in fourth; John Frankenheimer's "Year of the Gun" opened with a lame $730,000 on 739 screens, and "29th Street," starring Danny Aiello, bowed to a modest $450,000 on 131 screens.