Try activating Vista's hidden administrator then taking ownership.
The hidden administrator is the most powerful user, so remember to disable it after you have finished with it.
A tutorial from the How To Geek:
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When you DO change your permissions: (DONT DO THIS ON A ROOT FOLDER.)
You need to use the security tab and take ownership of the files.
Right click on the relevant folder, click properties->advanced->owner->* click edit. Make sure the "replace ownership on subfolders" box is selected, select your account from the provided list and click ok.
Note it should say you may need to reopen the folder for the permissions to fully take effect, that should fix things, it's quite a common issue...