Could this be a potential whole in Windows XP

In windows as we all know their are ways to share folders on a network. These folders are called shares. These shares can also be hidden from other users to see them. If a dollar sign ($) is used then the share can not be seen.

With windows upon its install it automatically creates one of these shares that cannot be seen. The only problem with this is that it is always called C$. If someone was to browse out to your computer from the workgroup in a small organisation. Are they able to browse through that share seeing as they know the address, to the share.

So if confidential information that the boss can only see is stored on his machine, who can read it? What could this do to the organisation?