VPN Connectivity…

I have one Windows 2000 server and i configured it for RRAS for vpn connection from remote location. That Windows 2000 server right now i configured in a workgroup not as a Domain.
My Probelm is : When i tried to connect this VPN server via dial up, its successfully authentycate me, after that its ask me for username/password with domain.
but i have query that machine is in workgroup not as a Domain.
So is it require that machine will configured as a domain ?
Awaiting your reply soon,

im available on chetanl@contechsoftware.com

Thanks in advance
Chetan Limbachiya