[pptp-server] Problems routing into local network

[Faralla]

Hi,

I installed pptpd on my linux-fw-box. I tried everything using a
modem-connection and everything seemed to work fine.
I could connect to my 192.168.0.x-subnet from the VPN-connection
(192.168.1.x IP) an vice versa.
Now a friend of mine connected using the VPN, but he can only ping the
fw-box, other machines in the 192.168.0.0-subnet are unreachable.
The only difference I could figure out is, that my friend is connected to
the Internet directly via LAN and not via modem like my test-setup.
Could anyone give me a hint how to solve the problem? All Clients are using
Windows 2k.

Thanks,
 faralla