Sharing ONE and only ONE folder

This is my scenario:

I'm running Win XP on one computer and Vista on another.
On the Vista computer I create a new folder on my desktop called "Test".
I right-click this folder and share it.

From my XP computer I open my network and get access to my Vista computer.

Then something strange happens:
From my XP computer I can see the Vista computer and I can see one folder
called "Users". Inside this folder I can see and access a lot of folders. I
can locate the new folder I created in Vista ("Test") under
"\\VistaPC\Users\MyUserName\Desktop". But I can ALSO see and get access to
all the other folders on my desktop, not only the "Test" folder I created
earlier.

I haven't created a share to "Users". I haven't created a share to all of my
folders on my desktop - ONLY to the "Test" folder.

Can someone explain to me why this is happening??

If I do the opposite, that is create a folder on my desktop on my XP
computer then I can see and access THAT folder from my Vista PC, but ONLY
this folder and no others.