As a non-EU citizen, you have our condolences; you will need to get that Spanish driver?s license after all. Depending on your nationality, non-EU driver?s licenses may be valid for the first year after arrival in Spain. After that, you are officially required to have a Spanish driver?s license. (Some expats, however, have been known to use their home-country license for years without problems. Not recommended, but possible.)
For US drivers, bear in mind that because each state has its own rules, foreign countries make agreements with individual states! That means that your New York driver?s license is valid (for the first year) in Spain, but your Massachusetts driver?s license is not (whether the police know which states are valid is another question).