Each airline may have different regulations / fees for travelers who want to travel with their pets. (But no, you don't need a passport for your pet.) You can either call your airlines directly or research on their websites... Just go to their main websites, and then type "pet" in the search area... Not sure which airlines you're using.. Here are some examples:
American Airlines:
http://www.aa.com/content/travelInfo...WithPets.jhtml
Northwest Airlines:
http://www.nwa.com/services/shipping...2.shtml#reqdoc
Delta:
http://www.delta.com/travel/special_...avel/index.jsp http://www.delta.com/care/faq/travel_faq/pets/index.jsp
Hope this is helpful...