As you may know, Windows automatically creates an administrator share for the system drive (such as C$) which is hidden by adding a dollar sign to the end of the share name. You can access this “hidden” share of Windows XP from other computers. However, by default, you can’t access this share of Windows 7 or Vista due to User Account Control (UAC).
Nevertheless, there’s a registry key to enable the same behavior as Windows XP in Windows Vista and 7:
Value Name: LocalAccountTokenFilterPolicy
DWORD Value: 0 = prevents access, 1 = enables access.