My suggestion for a first read is the Magical Disney Cruise Guide from Allearsnet.com. Click here for it. It is free and full of great information.
A good book is the Passporter Guide to Disney Cruise Line.
Then go to the Disney site. www.disney.com and click on the the Disney Cruise Line link. That will let you put in your preferences (dates, number of people, category, etc.) and give you costs. Once you have those costs and have made up your mind my recommendation is to contact Dreams Unlimited (the sponsor of this forum) and get a quote from them. They have fantastic services and we've booked 4 different cruises through them.
Last but not least - ask questions. Those of us who have cruised before are here to help!
We have the paperback copy of the Passporter & it helps to put everything in one place. We have taken it with us on both of our cruises. It got used alot more on the first one but we will still take it along this year.