Password protect

can I make it so in order to open a folder the user has to enter a password?

I want to do this so the passsword has to be entered no matter if your the owner or not

Hmm... what you're asking for is kinda difficult. If you want to encrypt certain files, you can use OS X's built in FileVault to encrypt your home folder.

Also, you can set the permissions in the terminal. However, this isn't quite what you're looking for either. If you know enough about the terminal, you could write a shell script that would automatically su to a certain user.

Lastly, there's parental controls built into Mac OS X. But I doubt you want this.

one option is to just remove the folder and replace it with an encrypted disk image, then to access the data the user must mount it by entering a password (which can just be stored in the users key chain)

another option is to add a new group using net info, then change the permissions of the folder so that only that new group can access it, then you can use net info to add some certain people to that group, these people will then become able to access the folder, all other people will have no access, I think you can also pass-protect the group (thou i have never done this) allowing any user to authenticate as the group and access the folder