Passwords for what purpose?
If you're storing them in a keychain, then the best you can do is encrypt them (preferably salted) and only decrypt as little as you need to use them. But as moritz says, anybody with system access can get to them.
If it's passwords supplied by users that you're storing to authenticate them later, you salt them and hash them with a one-way function and store that, then for authentication you take the user input, apply the salt and one way function and compare that with the stored one. You can make things harder by making the hash take longer.
