Problem setting up VPN connection using D-link DSL-G604T router

Hello,

i am trying to set up a vpn and am using the D-link DSL-G604T router,
but not having much luck!

i can connect to the vpn from the local network i.e. connecting to
192.168.1.XX, but cannot connect to it using the outside ip address,
i.e. going through the router. i have forwarded the ports for vpn
(ipsec l2tp and pptp) to the computer i am trying to connect to. i've
also tried enabling dmz for the computer.

i have trawled the internet looking for more info, but still haven't
been successful.
am running out of ideas! can anyone offer any advice please?

any help would be much appreciated.