Some of the plots are totally different. There was no scene in the book with Jeeves pretending to be that one woman author in drag. In the book everyone thinks the author is a little old granny lady because of the books she writes but she shows up, turns out to be a hot babe and she and Stilton Cheesewright run off together.
Also, the line "tried to pinch a bus" in the first episode was "tried to pinch a lorry" in the book but they must have wanted to avoid the pun. And in the book that was a big salmon in Bertie's room that the cats ate, not a little goldfish.