So you want a Virtual Networking Card to play with?

There is a feature inside Windows 2000, XP, Vista, and possibly others, called Microsoft Loopback Adapter.

To add one of these virtual adapters do the following:

1. Go to your Control Panel then choose Add Hardware.
2. In the Add Hardware Wizard, click Next.
3. Wait for the wizard to fail on finding new hardware attached to your PC but not added
4. Choose, Yes I have already connected the Hardware. (No will exit the Wizard).
   
5. Go to the very bottom of the list and choose "Add a new hardware device" then click Next.
   
6. Choose "Install hardware that I manually select from a list (Advanced)"
7. Choose Network Adapters
8. Under Microsoft, choose "Microsoft Loopback Adapter"
9. Click Next, then Next.
10. Then after it completes, choose Finish

Now if you go to your Control Panel then Networking Connections, you now have a "new" network card that you can use with Virtual PC or VirtualBox. You can also use it for various tests you need to perform, but don't want to screw up your actual Network Card. The list of what you can do with Microsoft Loopback Adapter is just so long, that if I tried to even list all of them, I couldn't and even if it was attempted, the list would be extremly long.