Swimming and surfing
Hi Mondo, welcome to Surfing Waves.
The general rule for how well you need to be able to swim when surfing is 'could you swim back in to the shore from where you are surfing if you did not have your board'. If you can do this then you can swim well enough to surf well. From a safety point of view you want to be a good swimmer just incase - the sea can be an unforgiving place.
Surfboards are like big buoyancy aids and will always help you to get back in to the shore - pretty much any strength swimmer will be pretty safe in the surfing school arena. In small waves there should not be a problem.
If you are looking to get into surfing and will be surfing regularly, and are not completely comfortable with your swimming standard then get yourself down to the local pool and start doing some laps. This will not just improve your swimming but your overall fitness - all the better for surfing.
Good luck with the surfing lessons - let us know how you get on.