I've only done it once, but here are my notes:

    VPN via PPTP Protocol in Windows NT with DSL Internet
Connection

1.  Install the Point-to-Point Tunneling Protocol in NT Control Panel

2.  Re-apply the current Service Pack.

3.  Install the Remote Access Service.  (My Computer | Dial-Up
Networking).

4.  Re-apply the current Service Pack.

(Steps 1-4 apply to both server and client)

5.  On the client machine, create a new phonebook entry in My Computer

the Phone Number, and dial using "RASPPTPM (VPNx)".  Network protocol
should be TCP/IP.  TCP/IP Settings as specified by the system
administrator for the domain.  (Usually "Server-Assigned IP Address").
Security set to "Accept any authentication including plain text,"
unless otherwise directed.

6.  User must have Dial-In permission on the server.

7.  Internet connection must be active in order to use the VPN
connection.

8.  User must log on to the remote client with the same user name and
password used to normally log on to the domain.  The RAS logon must
include the server domain name.

9.  After successful login, manually run any login or drive-mapping
scripts which normally run on the user's local machine in the domain.