Question about multiple users

Is it possible to set up WordPress so that certain pages were only viewable to registered users and others were open to the public. I’m not sure how to handle users frankly. I would just like to have a simple login box at the top of the page, similar to the way wordpress.org is set up rather than a separate login page. Is this even possible with WordPress, or should I use WordPressMU? Thanks in advance for any help.