The biggest challenge when making the jump from hiking to backpacking is the extra gear and weight. Start working on a list of what you think you will need. REI has some pretty decent printable checklists for this that would be a good starting point. Make sure to add up how much all that crap weighs (including food/water). Take a hike with it all loaded up to check weight. Cut out what you can and then go for it. Maybe an overnighter first to help decide what you can or can't do without.
Good advice on just an overnight first. I started looking up everything on the flight back two days ago. It seems like a large amount of stuff but it also all makes sense.
The first thing I need to get is a good pack, fill it up with crap and start walking with it. I loaded up a backpack with ten pounds last night and did three miles on the treadmill but honestly think that might hurt in the long run. Poor form, etc. so I scrapped it and now just back to walking and jogging with no weight until I can research and buy something decent.