Katie Holmes and Christina Aguilera have signed on to star together in a new movie. The Hollywood A-listers will team up for the family drama Humboldt Park. The film will begin shooting in February 2008 – just weeks after Xtina is due to give birth to her first child. We hear: “(Holmes) is trying to prove she can do more than fluffy popcorn movies,” and starring alongside the Fighter singer “shows she’s willing to take risks.”