This is how to enable the $admin share in Windows 7:
First, Folder and Printer Sharing must be enabled. Open the Control Panel, and select Network and Internet. Then click on Network and Sharing Center.

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Look to the left side of the Network and Sharing Center, and click on Change advanced sharing settings.

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In the new window, you can change each network’s sharing settings (Home, Public, and Work/Domain). Expand the profile you want to modify, and click on “File and Printer Sharing”

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Save your changes.
Next (I know, I wish it was just that easy…) you have to add a registry key. Open Regedit, navigate to HKLM\Software\Microsoft\Windows\CurrentVersion\Policies\System – create a new DWORD:
LocalAccountTokenFilterPolicy with the Value of 1

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Reboot. You can now access the $admin share remotely.