probably something like this:
! PPTP control protocol is carried in TCP using port 1723
ip nat inside static tcp 1723 interface 1723
! Let GRE traffic, PPTP control traffic and any other desired traffic thru
ip nat inside source list PPTP interface overload
ip access-list extended PPTP permit tcp permit gre any any ! Tighten this up once you get access working permit tcp any any eq 1723 ! Tighten up afterwards deny ip any any ! To be able to see acl match counter for denied traffic
interface ip nat inside ip access-group PPTP in
interface ip nat outside Ip access-group PPTP in