This is, definitely, not a hack for Google to hate this post. This will just teach you how to copy and retrieve the files that Books.Google.Com temporarily saved in your computer before showing it to you through internet browser.
Just follow the steps bellow:
1. Open your Internet Explorer (Not Firefox). Make sure that you are the admin of your computer. Then, go to the page in books.google.com that you want to download.
2. Now, go to “C:Documents and Settings%your admin name%Local SettingsTemporary Internet Files” of your computer. Delete all of the content of that folder.
3. In your Internet Explorer, refresh the page and browse-thru the pages of the books that you want to download.
4. Refresh the “Temporary Internet Files” folder. Copy all PNG files to another folder. You can distinguish PNG Files through its icon.
These files that you have just copied are, actually, the pages of the books that you have just browsed.