When we went to Mexico, we got information from this website:
www.pettravel.com It's very informative and gives you updated information based on what country you want to visit with your pets. We went to Mexico and had all of the documents in place, so getting through customs was rather easy. The rabies issue is one that you will need to research carefully based on where you are going. Your vet should be able to help you with this too. We flew on United and didn't have any problems.