All I can say is, bring lots of money. Pamplona and the nearby area is fairly expensive. Decent places will go for 300000 - 600000 pesetas per sq meter in the city. Nearby cities same or higher.

Doesn´t the Diario de Navarra have classifieds on line? Check www.diariodenavarra.es

In any case, you shouldn´t have a problem finding a place for the short term - room/apartment.