Accessing the shared resource on the XP from Windows 7

HI

I have two networked computers belonging to the same workgroup: one with Windows 7 Ultimate SP1 64-bit and the other with Windows XP Pro SP3.

On the XP computer, I shared a folder allowing only the access to the Administrators group.

Now, from Windows 7, I can see this shared folder, but when I try to use it, the no authorization message is displayed.
Why the Login window is not displayed?

THANKS

BYE