I do know, because I had my degree converted into a Spanish degree. Initially, the Ministry doesn recognize your degree as valid for teaching formally at a school here. You have to have it "homologado" which means you have to find a Spanish equivalency.
To teach in Primaria, you need Magisterio. If you have an degree in education in the States, that helps, but you still have to go through with the process. This requires patience too!
Of course, this also depends on how long you plan on teaching here. If you are talking about just a year or two, the Spanish government does have an agreement with the U.S.to bring in Americans with a college degree to teach as assistant teachers...mainly conversation classes.
What were you thinking of doing?