Password Protecting Folders That Are Network Shared

[mechanism]

I can access my entire network remotely - i.e. from my work office I can access my home network and the computers on it. However, I would like to tighten up security a bit by placing different passwords on different folders. This would keep an intruder / hacker from browsing freely over my network should he get into it.

So, specifically, I have a mounted folder under /mnt that I would like to add a password to. When completed, I would like for this to be my work flow when accessing my network remotely:

(1) Connect to my network (let's say via sftp)
(2) Browse to the /mnt folder
(3) Double Click on the folder that represents my "My Documents" folder on a Win XP machine on the same network
(4) Authenticate using a different password than the one I used to log in to system with sftp client.
(5) Browse the folder after password is entered.

Does anyone know how to set this up?

Thanks,

M