Actually, I'll be starting Nakita on leash training too. The best thing you can do is introduce it slowly. A figure 8 harness is better than just the collar. Start off with letting the cat smell and get use to the collar. Once they are use to that, put it on them for short periods of time around the house for a week or two. Then attach the lead to it and let the cat run around the house with it on.

Once the cat is use to the harness and the leash you can go outside. Again, it's through slow introduction and alot of praise to make it work.

But then again, some cat's would die first before being seen in public with a harness on. Then it would show the human has won!