Google temporarily saves book pages to your computer as PNG images in the cache, before showing pages in the web browser.
To save the pages, just follow the steps below:
1. On your Windows XP computer, open Internet Explorer (not Firefox, Chrome, Safari, etc). Go to the page in books.google.com that you want to download.
2. Go to “C:\Documents and Settings\%YourUsername%\Local Settings\Temporary Internet Files\” of your computer. Delete all of the content of that folder.
3. In Internet Explorer, refresh the page (press F5 on the keyboard) and browse through the pages of the book.
4. Refresh the “Temporary Internet Files” folder (again, press F5 on the active window). New files should appear in the Windows Explorer box. Go to View > Details, so that you can see the size of all the files. Copy all PNG and/or JPEG files larger than about 90kb to another folder on the computer. (If your computer has file extensions hidden, you can distinguish PNG and JPEG files through the photo-like icons).
These files that you have just copied are the pages of the books that you have just browsed. To "save as PDF", open the images in any image viewer or photo program, go to File > Print and then pick your PDF software as the printer. (If you don't have PDF software, you'll need to get some. I suggest the freeware CutePDF program.)