for using PPTP you have to create local users first. It is a good idea to assign static addresses. Switch PPTP on and use strong encryption, make sure that your clients support it, if not get an update!
In addition you need filter rules allowing the PPTP addresses access to your local network. (e.g. PPTP-users ANY local-network ALLOW)
You can use IP addresses of your LAN. ASL automatically sets host routes and answers ARP requests for this IPs.
BTW the VPN howto was written to use IPSEC clients and it is up2date :-))