Creating a VPN Server on Windows will require enabling Routing and Remote Access Service (RRAS). This service will not start unless you have at least two network connections. The purpose of RRAS is to pass packets between IP subnets. It basically turns your Windows workstation or server into a router. Normally, when you have only one network interface, any attempt to enable the service will fail.
To get around this requirement, a virtual network adapter can be installed. This software-based NIC is called Microsoft Loopback Adapter. To install the Loopback Adapter, you can follow the instructions below. This step-by-step, like all the others in this article, follow the wizards and consoles installed in Windows 2000. The wizards and tools on Windows XP Pro and Server 2003 are similar. The instructions below provide enough information to configure utilities on those operating systems with very little modification.