From personal experience ... we were trained 'in-house' by our own training dept and did the standard (?) CAA/BAA test questions.
I agree with 'ReadyToGo' in that it is reasonably basic ... speeds, heights, restrictions, where you can go/not go, and so on. However, like any acedemic subject, passing the test does not mean that you're any good. You need a while to get used to the airport environment, learning the road layout, where everything goes to, how to get from one place to another when the most obvious route is blocked.
One comment that I would add - in the UK you need to already hold a UK driving license. They're not teaching you how to drive, they're teaching you how to drive a vehicle at the airport.