The HBO family was out in force at Monday night’s premiere of “Warm Springs,” starring Kenneth Branagh and Cynthia Nixon in the story of Franklin D. Roosevelt’s polio-stricken days prior to becoming president.“Sex and the City’s” Michael Patrick King and Kristin Davis played catch up, while HBO Films prexy Colin Callender worked the room. However, Callendar remained tight-lipped when it came to discussing the new, nameless New York-based studio from the paid cabler and New Line. (“We’re going to do it, then we’re going to talk about it.”) And although there have been comparisons between the freshly formed studio and the old Miramax of the 1990s, he resisted being labeled as the new Harvey or Bob. “We are the new ourselves,” Callendar said. Branagh, whose next Shakespearean project is also being financed through the paid cabler, noted, “It is an interesting time to be with HBO. I think they are being very careful about expanding and how they do it. They are very filmmaker-friendly, and I think that means it’s likely to be exciting, at the very least, and hopefully successful.” Other HBO alums in attendance included “Springs” executive producers Mark Gordon and Celia Costas, and thesps Jason Alexander and David Paymer.