He'll come around in time. They may never be great friends, or they may be cuddled in each other's arms in a week. To speed up the getting used to process, you might bring the kitten out and let Snowball see him and get a good smell of him, but be on guard in case Snowball tries to hurt him. Be aware, though, that if Snowballs tries to strike at the kitten, a little swat won't hurt the kitten and will help Snowball feel like he is boss, and he will be more likely to not feel threatened. This will allow him to more readily accept the kitten. So be on guard but let cats be cats to a degree.