In addition to the requirements mentioned (What requirements do you have to meet to drive in Spain?), tourists using their own car should be aware that they may be need to show any of the following:
Temporary vehicle registration:
You may request it in customs. This permit has a period of validity of six months.
Vehicle insurance:
If you are a citizen of a EU member state, Switzerland, Norway, Iceland, Liechtenstein or Croatia, then you only need to have with you your insurance policy accompanied by a payment receipt to show the policy is current. If you are a citizen of Albania, Andorra, Bulgaria, Bosnia-Herzegovina, Belarus, Israel, Iran, Morocco, Moldavia, Macedonia, Romania, Serbia and Montenegro, Tunisia, Turkey or the Ukraine, you must use the Green Card (International Motor Certificate) system. If you are not a citizen of any of the aforementioned countries, you should take out a Frontier Insurance Policy (a temporary civil liability policy, obligatory for motor vehicles).
Since conditions may vary, we recommend you contact your local Spanish Consulate or Embassy for more information on these requirements.