Hi,
According to your description, I recommend you using Network Policy to enforce specific user accounts and domain
members’ account access the VPN server.
More detailed information, please refer to the links below:
HOW TO: Provide Secure Point-to-Point Communications Across a Private Network or the Internet in Windows Server
2003
http://support.microsoft.com/kb/324747
Dial-up and VPN remote access
http://technet.microsoft.com/en-us/library/cc782585(v=WS.10).aspx
Enabling remote client access over a VPN connection
http://technet.microsoft.com/en-us/library/cc995159.aspx
Configure Policies for VPN Enforcement
http://technet.microsoft.com/en-us/library/dd314165(v=WS.10).aspx
I hope this helps！
