How do you lock specific folders in Windows 7 without having to specify user privileges?

How do you lock specific folders in Windows 7 without having to specify user privileges?

I have an external hard drive hooked up to my Windows 7 machine, and I would like to lock a folder with a password so that nobody can access it through my computer (or any other USB-connected machine) without knowing that password. Otherwise, I would like to keep all the other data public.