pptp masq and or nat problem

Hi there.

I´ve got a 5.1.2 running at a client who want to tunnel a net through a pptp vpn.
I can succesfully connect the 5.1.2. via pptp to the pptp server over the net.
I´ve added the routes needed and can now also ping from any client behind the local gw to a server on the other net behind the pptp server. So it looks like all routes are ok. But when i try to setup a rdp session to a win2000 server it times out. On the server i can see a connection comming in but it looks like the communication back to the client is blocked by e-smith. Should i adapt firewall rules? plz. help.

Thanks
Edwin