I found this great short video showing the lovely scenery and what you can expect when driving your Spain rental car across the border into France. It looks as if they are approaching some official border crossing just as the video ends, but this is actually just a toll booth. The point where the France car hire crosses the border into Spain happens around 37 seconds into the video.
Though as you can see, there is not much you will need to prepare for when crossing the border into Spain in a rental car, it is important to make sure you have the money for toll booths. We have several travel guides that suggesting ways to reach various cities of interest in Spain such as How to Get to Almeira, How to Get to Madird, or How to Get to Bilbao. Once you arrive you can book a Spain car hire in any of these cities.