"Network Isolation for Metro style Apps" is a free Microsoft document which is focused exclusively on apps for the new Metro platform in Windows 8, and not for traditional desktop programs.
"With network isolation, developers can define the scope of the network access required for each process, which prevents a process without the appropriate scope from accessing the specified type of network or connection," Microsoft explained.
"The ability to set and enforce these boundaries ensures that compromised apps have access only to networks they have explicitly been granted access to, significantly reducing the scope of their impact in other apps or the system itself."
You can download Network Isolation for Metro style Apps here.
Here is guide in read-only mode: