Question : Router - Router PPTP VPN troubles

I have two networks at different physical locations.  Each have an ADSL Router to access the Internet which they can do fine.  

--1st Network--
Switching Device : NetGear 10/100mbit 8-port Switch
192.168.1.1 : ADSL Router / Firewall (Plexuscom ACC200, 1 Ethernet, 1 USB)
192.168.1.2 : Windows 98 Client
192.168.1.3 : Windows 2000 Professional (VPN Server)
192.168.1.4 : Windows 98 Client

--2nd Network--
Switching Device : Surecom EP-808AX 10/100mbit 8-Port Mini Switch
192.168.7.1 : ADSL Router / Firewall (Nokia Ni500 1 Ethernet, 1 Serial Disgnostic Interface)
192.168.7.2 : Windows 98 Client (VPN Client)
192.168.7.3 : Windows 98 Client

On the 1st Network, I have configured 192.168.1.3 to accept incoming VPN connections.  The Plexuscom ADSL Router also forwards all necessary VPN ports (TCP 1723, UDP 47 etc.) to the Win2000 machine.  Both ADSL connections are currently running with dynamic IPs, but 192.168.1.3 on the 1st Network runs a Dynu client program to host the domain "nzsnowboarder.dynu.com" under whatever the IP changes to.  This method has worked when dialing up to the domain from the 2nd Network using a 56k Modem, I was able to successfully establish a VPN connection after connecting to the Internet through my ISP.  There is no such client installed on the 2nd Network (so far it has been unneccesary to).

However, when I attempt to connect using the Nokia ADSL Router - I am kept waiting at the "Verifying Username / Password" dialog box until an Error 650 occurs (The computer you're dialing in to does not respond to a network request).

I was under the impression that the Plexuscom ADSL Router was not correctly routing the GRE packets correctly to the VPN host, however in light of the fact a dial-up connection was successful I find this unlikely.

I have installed various network monitoring software on the VPN host to attempt to gain some insight as to what TCP / UDP connections are being received when the client is trying to connect.  So far there has been no activity (of course, there was when the dial-up connection was established).  With this in mind I am inclined to suspect a forwarding / routing problem before the signal reaches the host.

Could it be that I need to configure the routing tables of each ADSL router to bridge both connections?  If so, is there a way which I can do this without the need for static IP addresses?  Also, the Plexuscom router supports NAT, NAPT, and Dynamic NAPT.  Could these help?

I would greatly appreciate some advice on how to set up routing table entries, I have not been able to fully understand the purpose of the Destination IP, Gateway, Subnet in their respective contexts.  While I am familiar with networking in general, routing tables are currently beyond my comprehension.

My thanks in advance for any insight you may have.  A generous 445 points is available to the one who answers my question successfully.

Answer : Router - Router PPTP VPN troubles

PAQed, with points refunded (445)

modulo
Community Support Moderator