Selecting specific computers in "Locations"

I have already setup a network between Windows 7 x64 Ultimate machines. However, I am adding more computers to the network and would like to select as to which computers can see a particular folder. The problem is that when I am trying to set the permissions and go to "Locations," the only computer listed is mine, even though the "Network" folder clearly lists three other computers. How can I get these computers to also appear in "Locations" so I can choose which ones to share my files with? Ideally I am trying to create a new user group that will consist of preselected computers.

My only other option is to share the folder with every authenticated user on the network, which is not something I want to do. I'd like user X to get access while user Y be denied.

Thanks for any input.

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