If you get Cat Fancy, my article about harness training appeared there last month.
Basically, it boils down to this; not all cats are good candidates for harness training. You need a younger, or an outgoing cat, and when you put the harness on the first time, you don't fasten it. You feed while the cat is wearing it. Then remove it after the meal. Repeat that procedure a few times more for however long it takes for the cat not to react to it. If your cat is "going nuts" then he is probably not a good one to take outdoors. Many harnesses are made so the cat can easily slip out of it, so if your cat freaks outside, you could lose him. If the cat isn't bothered by the harness, than taking that cat outside becomes a real possibilty. But food and reward are key when training a cat to accept a harness.
About the hissing, if this cat is new, advise you to back off and not approach or initiate contact. The cat needs to get used to his new environment, and although you may want a lap cat, that is the furthest thing from this cat's mind at the moment. Also do not stare into the cat's eyes for any reason. If you make contact, close your eyes and blink slowly then move away. Staring means you are ready for battle and your cat will answer with claws and teeth at the ready.