To transfer eBook to iPad

Download the eBook on your desktop first and then transfer it to iPad.
Follow the link to see how to download eBook on desktop:
http://mpsbookstorehelp.blogspot.com/2011/11/steps-to-download-ebook-on-desktop.html

Steps to transfer eBook to iPad are: 

•  After the file has finished downloading, Launch iTunes by clicking its icon.
•  Click to select Add to Library from the File menu.
•   Select the eBook file from your Desktop and click the Choose button.
•   Click to select Books from the list of libraries on the left.
•  Connect your iPad to the computer and select it from the list of devices on the left.
• Click to select the Books tab.
•  Check the Sync Books check box if it isn't already enabled. If all books are selected then all your Books will be transferred to the iPad. If selected books are selected then you will need to look below for the newly added Book and check the check box next to its title.
•  Now click the Apply or Sync button at the bottom right of the window. You may receive a warning that this will erase all the books on your iPad if this is your first Books sync. Click the Sync Books button.
•  Once the sync has completed you can open i Books on your iPad to read your newly transferred title.
• If you do not have i Books on your iPad you can download it free from the App Store.