I'm new to Civi and I'm trying to view books.civicrm.org, but its asking for a username and password, where do I register for that?
I'm guessing there is a dns problem somewhere. Depending on where you are in the world and what your dns server is you might be getting directed to the wrong site. Civi did a server migration recently so the problem might resolve itself in a matter of hours, or you might switching to a better dns server, or you could go directly to http://gitbook.civicrm.org/ as JoAnne suggests.
If you are after civicrm documentation the address is book.civicrm.org (ie no "s" on book). That takes you to a page which directs you to various documentation.
(If you are looking for the user and admin guide for v 4.6 you can go directly to gitbook.civicrm.org.
Did you find that URL somewhere on the civicrm site? If so, please let me know where it was so that it can be corrected.