If it's the latter then I'm surprised there aren't already cheap plugin systems for Wordpress that would do the same thing.
I didn't realise that OpenTable has a whole booking.com style website, including the "booked 15 times in the last microsecond!" nonsense. Feeling somewhat like a luddite now, I've only ever used it when trying to book a table at a specific restaurant (i.e. via the restaurant's website).