Actually, it's best to separate new kittens/cats when brought into the house. Cats are territorial, and the resident kitty needs to get used to the idea that there's another cat around, and the new cat/kitten needs a little time to adjust to the new place, new smells, new sounds, new people, etc. Being in a separate room for a few days/weeks (depends upon the cat) helps give them time to adjust so they don't feel completely overwhelmed, and helps create a "safe space" they can retreat to when you do open the door.
Here's a good article on introducing new kitties: http://www.thecatsite.com/Behavior/4...cing-Cats.html
I'd go ahead and separate them, at least for a day or two, if you have the space to do it (even a large bathroom works). Let them smell each under under the door.
Wipe new kitty all over with a wash cloth, and put it under resident kitty's food dish. Do the same for resident with new kitty. This will help them associate "good things" with each other's scent.
Give your resident kitty extra play time - this will help work off stress. He's mad right now, but he'll get over it.
Give him extra treats and love. You can also take another cloth, rub it all over new kitty, and after a good play session with resident kitty, put treats down on the "new kitty" scented cloth.
Give it a little time, let everyone have some space and time to adjust. They'll probably end up being best buds.