Try keeping them in rooms that are separate, but perhaps connected by a door. You want them to get used to each other's smell. Let them run around the house whenever you can, too. It'll take some time, but they'll get along eventually. The kitten will adapt a lot easier than your older cat. My mother has nine cats, and they're only starting to get along now. Cats will really only be friendly towards each other if they've grown up together.

By the way, that kitten is adorable.