If you really want some good information, and don't know where to start, I picked up the book "The Conscientious Marine Aquarist" by Robert Fenner (Don't pay more than $20 for it). Some of the stuff is a bit out of date, but it will give you an idea where to start and how to approach the whole saltwater tank thing.
I suggest looking at the fishes first. This site and others categorizes the fishies by type, and have a whole lot of information about each species. I say make a huge list of your dream fishies. Everything you would ever want to see in your tank. Then start looking into which ones you can have together, which species you can only have one of, etc. Decide if you want a reef tank or not (if you want corals.) This will affect many of your fish choices. Look at your fish list and decide if you're leaning more toward an aggressive or passive tank. How much room the fish you really like need, and how many you want to start out with. I suggest start with the aesthetic part of the hobby: where do you want to put it, what do you want it to look like.
Also consider your budget.
These message boards are great resources of information, and can get confusing. I suggest searching certain fishes ... if you end up searching 'yellow tang' and keep finding threads about how all tangs get ich, that's something you need to consider. I also suggest that once you find your tank size, search the forums to see other peoples' pictures to get ideas about yours.
There are some good 'sticky' forums at the top of each forum category (the ones that constantly stay at the top of the list for a reason - they are extremely useful.) Good luck!
Don't forget to have patience. I suggest read up now. Everything you can get your hands on. Find the local fish stores (LFS) near you and ask them questions. The people that seem like they really know what they're doing - use your better judgement on this one. Get as many different opinions as you can, and only take the advice if it makes sense. If you don't have the patience and drive to research now, you're going to be too easily discouraged when something small goes wrong with the tank, and that something small can turn into something big very quickly. On the other hand, if you enjoy learning as much as you can about the fish and the corals and the hobby in general, then keep reading, learning and enjoying!