Routing questions

Hello,

I don't want to have two threads, so I made a Fup2 to
my first news at alt.os.linux.suse.
I hope this is OK.

I have a routing task here where I need some help.

All systems are running with SuSE 10.2 or 10.3.

All netmasks are 255.255.255.0

-System A has the IP 192.168.1.2 and 192.168.2.1 (this should be the router
between the two networks)
-Gateway for Network A is 192.168.1.1 which makes the Internet connection
-System B has the IP 192.168.1.3 and it is my VPN Server
-System C has the IP 192.168.1.10

the above is running as I expect.

But now:
-System D has the IP 192.168.2.2 with Gateway 192.168.2.1

System D is a remote system which I want to control from outside.
I want to connect System D via VPN and if I'm on System D I want to
have an Internet connection too.
But I don't want to be able to connect System D with System C (or other
systems in
Network A except System A and System B)

And all this should happened without static routes on System D,
just default routes and default Gateway.

Is this possible and if yes how?
What should I have to change or install on System A?
IP forward is enabled on System A.

Markus