In reply to mypyrex:
Are you buying excess insurance independently rather than through the hire company?
If so the hire company are likely to require a pre-authorisation on a credit card at pick up for the value of the excess. If you have any damage they take the cost out of this and you claim it back.
My experience suggests that unless you are doing multiple trips in a year it is cheapest to use the hire companies excess insurance as long as you have factored this cost into the process of selecting your car.