I really don't think having a residence permit for Portugal allows you to live in Spain. EU <i>citizens</i> can live in other EU countries, but a residence permit isn't citizenship, nor even a certain path to citizenship.

I should have been clearer. When I speak of living in Spain, I mean being a legal resident of Spain, without which you can't avail yourself of any services in Spain, or buy a car.

***and rental companies DO allow you to drive and rent cars with USA license regardless of time in the country.*** But you still need an I.D.P. which has to be renewed each year via the address on your US D.L.