I also recommend doing the classroom work before you arrive, but I'm not keen on PADI's eLearning. There is another way of doing it. But you're now probably too late for either.

But if you have any doubts about diving then take Wendy's advice. If you love it you can progress to a certification course - just tell the dive op before you start that you may want to do this (it affects the way they run the DSD).