Research TRUSTEDUSER which is a new thing. Only the trusteduser can delete the default wallpapers, among other things.
Sorry but I think all this will be in some books about Windows 7 administration.
I have always used Windows XP and did not buy into Vista until recently when I got a new laptop that came with it and later was upgraded to Windows 7. The laptop also came with a small partition called RECOVERY that was designed to restore Vista. Since I deleted it and installed Windows 7 I did not need that recovery partition anymore and decided to erase it and use it as a scratch disc for the Adobe products.
I knew about the admin access and UFC (or whatever it's called there) and I logged in as administrator and started deleting folders on that recovery partition (disc D:). It removed pretty much all the files and then, to my surprise, displayed a message that I do not have access to a group of certain files and that I need to have a permission from a TrustedInstaller, or something in that nature to delete it.
I did some quick Google search (painfully remembering people's woes with Vista) and found the way to change access rights for Windows users, but for some reason I could not neither find, nor add that TrustedInstaller, and my admin user account has all privileges checked except a grayed one that reads "Special privileges".
So, I'm totally confused. What is that TrustedInstaller and how come "it" has more permissions than me???