My two favorite ways:
- email the book to yourself, then open it in e-reader of your choice (I recommend Marvin)
- load the book into your cloud software (Dropbox, SugarSync, Copy.com...), then open it on your iPad
No need to mess around with Mac OS! And especially not with iTunes or iBooks. No need to establish a direct connection between your computer and the iPad to smoothly transfer books to your iPad.