Training a cat? Sure.

Yes! Cats can be trained. They can be taught house manners, just as dogs can. And they can be taught little tricks and "obedience" commands, as well. Of course, we'd never call it obedience when talking about cats. SHHHH! They hear that and that will be the end of any talk of cat training.
Seriously, the best way to train a cat is to be very consistent, very gentle and calm, and use reward properly. You can teach your cat to sit on command very easily. The first step is to find out what treats are favorites for your cat. The same is true for teaching your cat to lie down.
There is a new kind of tuna (for people) available in some stores -- I found it in WalMart. It is real tuna, formed into cubes, about 1 inch each. Tastes great, but holds together better than most tuna. My cats LOVE tuna, and this kind is very easy to use for a training treat. Look for it when you go shopping.