To fly into Mexico you HAVE to have a passport. As of right now the only way you can get into Mexico without a passport is by land travel, but that will change as of Summer 2009. As of Summer 2009 you will need a passport for any land travel into Mexico and Canada.
You can fly to Mexico, but, you won't be able to fly back to the US.
Yes, it is.
Yes, you do.
Yes you do.
Always.
You will need a pilots license, ID/passport to fly into Canada or Mexico.
yes you do. you need a passport to fly anywhere outside of the United States.
Yes, you do.
Yes they do.
If you are already in Mexico, sure you can.
You always need a passport to enter another country