If you've never read the book, then don't. Go see the movie first. If you can handle that kind of dry, complex British humor, then you'll be absolutely fine. Reading the book might set you up for expecting things you won't get, which seems to be the eternal fan problem when viewing adaptations. Give the filmmakers a chance to present their version without any expectations. I think you'll really enjoy it. Spike and I laughed big time!

I would definitely recommend reading it afterwards, however, as it is an absolutely hilarious read.