User Configuration\Administrative Templates\Windows Explorer
Also see the "Prevent access to drives from My Computer" setting.
This setting removes the icons that represent selected hard disk drives from My Computer and Windows Explorer. Also, the letters that represent the selected drives do not appear in the standard Open dialog box.
To use this setting, select a drive or combination of drives in the drop-down list. To display all drives, disable this setting or select the "Do not restrict drives" option in the drop-down list.
This setting removes the hard disk drive icons. Users can still gain access to drive contents by using other methods, such as by typing the path to a directory on the drive in the Map Network Drive dialog box, in the Run dialog box, or in a Command Prompt window.
This setting does not prevent users from using programs to access these drives or their contents. It does not prevent users from using the Disk Management snap-in to view and change drive characteristics.
Non-Microsoft applications that are certified with the Windows 2000, Windows XP, Windows Vista or Windows 7 operating systems must adhere to this setting.
With Win 7 ultimate you can set restrictions to a drive in explorer. Right click on the drive and goto properties and then choose the security tab. From there you can lock down based on id's, groups, etc. Read, write etc. Just as long as it's not your OS drive. You wouldn't want to lock someone out from all the apps and so fourth.