UAC created a unique problem for the laptop, intended to dual-boot XP and Vista. More precisely, it was dual booting until a recent “update” from Windows Update rendered the XP side inoperable with a blue screen complaining that registry could not be loaded. But that can not be blamed on Vista. (Yes in principle, one could load the crash dump in a debugger to investigate in copious spare time.) Attempting to rescue files creates an interesting problem, because accessing the XP file system requires exercising the “take ownership” privilege granted to administrator accounts in Vista. UAC gates the exercise of administrator rights, in keeping with least-privilege principle. Under XP take-ownership is applied automatically and would work seamlessly from Explorer. Browse to the documents folder of the other OS and you are authorized every step of the way, because access check logic helps itself to the ownership shortcut.
Under Vista, that doesn’t work. It leads to not one but 2 UAC prompts, after which you end up with an error message to the effect that getting access will require using the Security Tab. (Right click, Properties / Security.) It is here that the ownership can be changed to one of the accounts on the Vista side, and this has to be done recursively by checking “Replace owner on sub-containers and objects.” After a few more UAC prompts, the directory is open to browsing.
But the trouble does not end there– trying to open a Word document results in an access-denied message inside word. Ownership had been changed, but the permissions on the file were not updated and still referred to the non-existent accounts from XP installation. On the other hand, copying the files to a different location, for example to burn them on a CD, required a single prompt in Explorer, suggesting that it is up to each application to detect and work-around these error cases