Is he broke to ride? If so, it shouldn't be too hard. Before you have him pulling things though, you really need to get him to ground drive well first. To do that, I'd advise in having someone hold his head at first and lead him while you 'directed' from the back, gradually getting to a point where he was following YOUR commands.
Please be careful though, driving is a very dangerous sport, especially with a horse that doesn't know what its doing and a driver who doesn't know how to tell it what it's doing!