Before you do anything else, you definitely need to read the articles mentioned above. Fish keeping is part zoology and part chemistry. To keep healthy fish, you need to make sure to have an ample amount of beneficial bacteria in the filter media before adding fish. Also, browse your lfs to see what kind of fish you might want to have. Employees there should have at least a basic knowledge of which fish can go together. I'd get some ideas there and then post here before actually buying anything. If you don't want to go through the weeks of fishless cycling, I'd recommend using Tetra Safe Start. I've used it on both my tanks and had good results.