I'd start with learning about photography: Understanding Exposure by Bryan Peterson. This is an acknowledged classic.
Then you might be interested in something about the camera itself; there are a wide variety of opinions on this, but I prefer Thom Hogan's The Complete Guide to the Nikon D5000 (or any model - he does them for every camera now).
For post processing, consider something like one of the books from Scott Kelby on the Adobe product of your choice (Photoshop Elements is a good start). There are many others, including CaptureNX2 from Nikon, but from my personal perspective Adobe's products are a more universal approach.
_____ Brian... a bicoastal Nikonian and Team Member
My gallery is online. Comments and critique welcomed any time!