Many pros steam seats, key is not to hot or not to damp. Search some of the dedicated detailing forums and there is plenty of info. As far as carpets go steam away just make sure they are dry when putting the inerior back together. Steamer also works wonders on door jambs if you are goign fore the tru show car detail.
08 E90 335i Monaco Blue Gray Dakota ZPP ZSP Heated Seats CA Step w/Paddles iPod