I had to search around for the answer for this. But in Windows 7 / Windows 2008, the administrative share access is taken away. I found out when trying to access certain computers using \\computername\c$ and no matter what credentials I provided nothing worked. The workaround is below.
Locate and then click the following registry subkey:
On the Edit menu, point to New, and then click DWORD (32-bit) Value.
Type LocalAccountTokenFilterPolicy to name the new entry, and then press ENTER.
Right-click LocalAccountTokenFilterPolicy, and then click Modify.
In the Value data box, type 1, and then click OK.
Exit Registry Editor.
The LocalAccountTokenFilterPolicy entry in the registry can have a value of 0 or 1. These values set the behavior of the entry as follows:
0 = build a filtered token
This is the default value. The administrator credentials are removed. These credentials are required for remote administration of the print drivers.
1 = build an elevated token
This value enables the remote administration of the print drivers on a server within a workgroup