How can I create a TAP virtual network device in Windows 7?
The TAP device acts as a bridge between the network and a piece of software. Creating a TAP device is easy enough, but it won't do anything by itself - it needs some software to handle the data that's passed to the network interface.
Creating a TAP interface is detailed here: http://www.varsanofiev.com/inside/using_tuntap_under_windows.htm
There's a sample C program there to show how software to work with it can be created.