Allow 1 user to access 1 server using PPTP and RDP

I have been tasked with the following this morning.

1 user from an external company needs access to a virtual server to do some SQL work. he is going to be dialing in from somewhere else using PPTP. I was asked to make sure he can only access the virtual server after he creates the VPN connection. (he is not aloud to access any other server on the network)

Can anyone tell me how this is done please?

Public IP = 123.456.789.123

Virtual Server = 192.168.0.95