VPN software for LT2P tunnel authentication

Windows comes with a VPN client built in, windows server has a VPN server built in... So can you explain the situation a bit more?

I agree with Aaron, clarification is needed on this as Windows come with configurable VPN clients/connections built into the OS.

as mentioned above, Windows severs come with built-in VPN support for both client and server over IPsec and PPTP. what you do is simply to follow the instructions to setup a VPN server using RRAS. see below the official technical document for details.

FYI - Checklist: Installing and Configuring an RRAS VPN Server
http://technet.microsoft.com/en-us/library/dd469733.aspx

Thanks for the help thus far, however, I am aware of Windows VPN abilities, but our requirement is somehow unique;
We have a service provider that provides us with a static IP, but for the static IP to work, we require L2TP "tunnel authentication" / "termination".

This is quite a unique feature and only a couple of router modules support this function.

An example of L2TP tunnel authentication / termination for router config;

•Protocol: L2TP VPN
•Type of connection: dial-out
•Server IP address: 196.30.xxx.xxx (this is a fixed IP address that you must supply)
•Connection type: Remote access
•Username: yourusername
•Password: yourDSLpassword
•Authentication type: PAP
•Tunnel authentication: enabled
•Secret: hxxx (this is a fixed secret for the L2TP server that you must supply)
•Activate as default route: yes
•Remote host name: (leave blank)
•Local host name: (leave blank)
•IPSec: not enabled
•Authentication: None
•Encryption: NULL
•Perfect forward secrecy: None
•Pre-shared key: (leave blank)

We've already tried a couple of routers with this VPN functionality, but all failed for various reasons;
I was advised by the ISP that as an alternate method, we can install VPN software on Windows server that supports L2TP VPN with tunnel authentication.

I don't think Windows supports this VPN functionality by default?