Windows 2003/VPN

Hi,

I have setup VPN on Windows 2003 Server. As I didn't have 2 NIC I configured Loopback Adapter and everything looks fine. I am able to connect to VPN Server and browse websites. But I am not able to setup multiple VPN clients to connect to the server. Only 1 user can connect at a time. This it what I need.

1. I want multiple users to connect to the server using VPN client.
2. I want to configure Routing and Remote Access in a way that 1 username should not be able to connect from multiple locations. e.g if user Test1 is already connected to the server through VPN client the server should not allow anyone else to connect through the same username i.e "Test1" from a diffrent location. But Test2, Test3, Test4, Test5 can connect at the same time.

Please let me know how to I go ahead and set this up?

Thank you for  your time and efforts!