Carpe Jugulum by Terry Pratchett and Stephen Briggs

The de Magpyrs are the sort of vampires that would have Count Dracula spinning in his grave: modern, forward-looking and no longer afraid of holy water, garlic, religious symbols or, indeed, of anything else. This makes them very, very dangerous. Luckily for the Discworld, the three Lancre witches are on hand - and the battle is on!