Some folders in Win Vista/7 are owned by TrustedInstaller and can't be modified even with admin right. Only way I know to get access to these files:
Windows 7 Starter edition does not allow to change the wallpaper of the desktop. Overwriting
the standard wallpaper image stored in
%windir%\web\wallpaper\windows\img0.jpg results in
a black background.
It is possible to change the wallpaper to any image you like
by setting the path into the registry key
You will actually never see the wallpaper, since you have to logout/login or reboot for the change to
take effect and the key is already overwritten during the login process.
In order to prevent windows from overwriting the wallpaper key, one has
to change the access right to the registry folder
and limit it to read only for everyone (right click on the above object and change the access
properties accordingly). One has to disable the inheritance of the access
rights from the objects parents as well!
The above procedure actually works, but has the side effect that the user can no longer change
some of the desktop properties like the color scheme and the screen saver. In order to change
these properties the access right to
HKCU\Control Panel\Desktop has to allow write
access for the current user. Don't forget to remove this access right again after the changes
have been done. Otherwise the wallpaper will be gone again!
Modifying the registry can damage your Windows installation and can render it useless. Edit the registry at your own risk and only when you know what you are doing!