Why would you need this?Well, if you need to log into a Mobile Workstation that you've not logged into before and you're not on your corporate Active Directory network. On Windows XP & Vista you do this by typing your credentials into the normal login screen and then you click the "log on using dial-up connection" checkbox, this lets you could connect to the VPN at your company and be authenticated.
So here is how you do it in Windows 7:
1)Logon to Windows using PLAP (Pre-Logon Access Providers) local admin. 2) Control Panel -> Network and Sharing Center -> Setup up a connection or network -> “Connect to a workplace” OR “Set up a dial-up connection”. 3) Check the checkbox to “Allow other people to use this connection” (so that the owner of the DUN configuration will be System and not your individual user). 4) Complete the wizard and save the connection. 5) Establish the dial-up connection/VPN then join the PC to the domain. 6) After rebooting, press Ctrl-Alt-Delete to log on and you will be presented with the logon screen for the user that last logged in. Press Esc or click Switch User to view other logon options. 7) There will now appear a blue button near the lower-right corner, just to the left of the red Shut Down button. Click the blue button. If you have more than one System-owned DUN configuration, then all of them will appear here as buttons that can be clicked, in which case you click the one you want to use. If prompted, type the username and password for the DUN connection and click the round, blue button to connect. 8) A dialog appears, showing the progress of the connection attempt. After the connection is established, Windows will use the same credentials to log into Windows. If that fails, the DUN connection remains active, and you will be taken back to the Windows logon screen to submit Windows credentials.