I would start out with the articles section on this forum. There are a few good articles that will get you started on equipment and cycling and all that.
A lot of the pricipals of keeping a tank will transfer over from freshwater. It is a little more complicated keeping an eye on your levels but nothing you can't handle if you are interested in salt.
I would warn you that most saltwater tanks are larger in general that freshwater because the more water volume you have the easier it is to keep your tank parameters stable. If you are looking to stay small for your first tank to try your hand at SW
i would suggest the 30 gallon range. There are a few biocube tanks that are in that size. The larger the better though. If you can afford/have space for a 75 i think this is a perfect place to start.
The upfront cost of SW
is quite expensive depending on what you want to do with the tank and how willing to DIY you are. There are a few things like buying base rock instead of live rock, and making your own sump instead of buying one that will cut down your start up cost by a ton.
I believe liveaquaria.com has an articles section as well with some basic information that is good for beginners as well. I would not take all their information as fact since they are still trying to sell you things but most of it is pretty good. Read up a bit on those and that will generate a lot more questions. Once you have some more specific questions start up a thread of them and we can help you from there.