Hi Francis: The bookport can use Compactflash memory of any capacity, which can be purchased from any computer store. I have had good service from memorysuppliers.com. Finding Harry Potter books may be more difficult because of international copyright issues. For that reason, I can't recommend Audible, although Audible would certainly have those books, as will Bookshare, which I also can't recommend for the same reason. Good luck. Cheers, Dave