For a true saltwater newbie I would not only recommend studying as much online as you can but also I would suggest you reference our Saltwater library. I know I know your on summer leave from college and you dont want to have to read another book till fall. But really a good book or two and a good website like this will save you hours of greef and also some of your cash.
I personaly have The New Marine Aquarium by Michael S Paletta and Conscientious Marine Aquarist by Robert Fenner. I feel these are two great books for someone just starting out in the hobby. If I was to chose between the two I would say the book by Fenner would be my top choice.
If you cant go larger than 30 gal
then remember a few good points. As Tim pointed out your maintinence schedule will be important. Regular water changes and daily toping off with freshwater will be important to maintan the water quality. With saltwater tanks when the water evaporates the salt stays in the tank so the net result is a higher salinity after a couple days of evaporation. On smaller tanks this change happens faster than on larger systems.
ALso its good to know that the amount of fish you can put in a tank is alot less with saltwater. A general rule of thumb that I like to use for beginners is 1" of adult fish per 5 gal
of tank capacity. So that would give you 6" of adult size fish to stock in your tank.