File sharing and VNC access problem

Hi
We have problem with file share and VNC connection to particular computer. This comp (192.168.0.31) Is behind mikrotik and RRAS, for ie:

192.168.3.200 (XP) ----> mikrotik(PPTP SERVER) -------VPN-------RRAS (Server 2003)-------->192.168.0.31

And when this is used:

192.168.3.200 (XP) --------VPN(PPTP)--------RRAS (Server 2003)-------->192.168.0.31

than we can do \192.168.0.31 with no problems.
Some of mikrotik settings:

/ip firewall nat
add action=masquerade chain=srcnat comment="" disabled=no out-interface=P2-telekom
add action=dst-nat chain=dstnat comment="" disabled=no dst-port=18389 in-interface=P2-telekom protocol=tcp to-addresses=\
    192.168.3.4 to-ports=3389
add action=dst-nat chain=dstnat comment="" disabled=no dst-port=1723 in-interface=P2-telekom protocol=tcp \
    src-address-list=!trusted to-addresses=192.168.3.4 to-ports=1723

/ip firewall filter
add action=accept chain=input comment="" disabled=no protocol=icmp
add action=accept chain=input comment="" connection-state=established disabled=no in-interface=P2-telekom
add action=accept chain=input comment="" connection-state=related disabled=no in-interface=P2-telekom
add action=accept chain=input comment="" disabled=no dst-port=1723 \
    in-interface=P2-telekom protocol=tcp src-address-list=trusted
add action=drop chain=input comment="" disabled=no in-interface=P2-telekom

I believe that in case when PPTP is used (on mikrotik) NAT is not interfering with packets going through VPN.

How to make correct configuration on Mikrotik?

Thanks