debian-firewall: routing GRE for PPTP VPNs.

[Brendan J Simon <brendan.simon@ctam.com.au>]

I'm trying to setup our firewall so that a remote user can access our
network via a Win2000 server (using PPTP).  I have ipmasq installed on
the debian firewall.  I can route the pptp packets through with the
following command.
$ ipmasqadm portfw -a -P tcp -L my.firewall.ip.address 1723 -R
my.win2000.ip.address 1723

How do I route the GRE protocol to the Win2000 machine ?
Do I use portfw, autofw or mfw ?

The VPN-Masquerade HOWTO says that the 2.2 kernels need to be patched to
allow GRE and ESP protocols to be forwarded.  Is the debian 2.2.17
kernel already patched for this or do I have to do it manually ??

Thanks for any help.  Please CC any replies to me as well as the list.
Thanks,
Brendan Simon.