The singer gets ready for her performance at the Rockefeller Center tree lighting. Plus: Clay Aiken, Hilary Duff, Paris Hilton and more

TEST RUN

Jessica Simpson keeps warm as she rehearses for her performance at the Rockefeller Center Christmas tree lighting on Tuesday. The singer performed twice at the event, singing "What Child Is This?" and a rendition of "I Saw Mommy Kissing Santa Claus."