Hi!
I am not a nurse, but I am a massage therapist who works in a hospital setting. I strongly suggest you check the specific licensing requirements for the state your practice in. For instance, in New York you need something like 500-700 hours and you are licensed as a healthcare professional. If you aren't aren't registered with the state as a licensed massage therapist and you practice masage, it's a felony offense.
However in California (where I live) you only need 140 hours for a minimum certification, but each city has their own requirements to practice (some keep it at 140, others go up from there...some don't even check). Again, it is important to know the regulations for the state and city your practice in. As a general rule, most massage therapists agree it takes about 500 hours of training to really develop your touch, learn a variety of modalities, and then master those modalities that work best in your practice.
Lastly, as far as just getting a book and practicing on patients is concerned, I think that is a dangerous amount of liability to take on. I doubt you would be covered if something went wrong. To be a nurse massage therapist implies working on clients and/or patients with a wide variety of contraindications, symptoms, and illnesses. Learning from a book is fine for a basic relaxation massage on a relatively health individual, but it would be a great dis-service to work on patients without more specific hands-on training and guidance.
There is a definate difference between relaxation/spa massage, and a more clinically centered massage for patients. That's another consideration: what type of population are you interested in working with? I always wanted to work with patients in hospital settings, but without the RN I had to jump through a LOT of hoops and additional training before I got there.
I've met many RN's at my massage school, and all of them have really valued their massage training. Going to massage school is a fantastic experience! Good Luck!!