Windows 2008 R2 Drive Root Minimum Permissions

See notes on Win2K8R2 UAC for allowing Administrator access to volumes, files and folders.

Changing permissions on the System partition (C:\) is never advisable

For all other partitions, suggested minimal permissions are;
Administrators : Full Control
SYSTEM : Full Control
Owner Rights : Read

Note:  Administrators may be prevented from accessing local drives with the EVERYONE group removed, by UAC policy settings.  To prevent this occurring, the group policy setting will need to be edited.

Policy: computer configuration\Windows Settings\Security Settings\Local Policies\Security Options
Run all Administrators in Admin Approval mode.
Default: Enabled
Change: Disabled