There are a ton of websites out there with tons of good info. You can get equipment more cheaply on ebay than you can in a store - and for saltwater stuff you're going to want to go to a places that specializes in that, not something like petco or whatever.
the key points are to make sure especially for your first tank that you don't get anything smaller than 50 gals, that you cycle it adequately before you add any fish (some people advocate cycling with one fish to help get it all going), that you have adequate light in an adequate spectrum for what you want to do with your tank (corals, for example need a LOT of light to thrive), that you don't get too many fish (a lot of saltwater fish are far more territorial than freshwater), and you always want to have far more filtration than you think you need. I've seen "saltwater" kits sold at petco that don't even include protein skimmers!
It takes a lot of planning to start up a halthy saltwater tank; I think your best bet is to read as much as you can about saltwater tanks (get a book, and then consult online. you can sometimes find differeing opinions, so you need to learn all about them) and then go to a reputable aquarium place and talk to the people there. That way you won't get talked into buying shit you don't need etc.
Oh yeah it's also a gazillion times more expensive than a freshwater tank to start up and maintain :)
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