The problem with using a password to prevent people from accessing your data is they could simply open your PC case, yank out your hard drive and slap it in a another PC as a slave. Then they can just browse all your files at their convenience.
I know there are several programs that allow you to create a virtual encrypted disk, but is there any that will work with your Windows password to let you just encrypt a certain directory or perhaps the entire disk, and you won't have to enter any passwords or mount/unmount the virtual partition.
E.g.: Once you log into Windows, it will automatically give full access.