> The routes on the lan's are set up correctly to forward traffic to the
> m0n0. I think it is part 2 that is having the problem. I can't add the
> route to the remote networks using the remote mono as the gateway as
> m0n0 then complains that its not on the local lan with the following
> information:-
> 

Typical routing issue: a given gateway *must* be on the local network. 
It must be the first router on the path. This explains the error message 
in the logs...


Example:

Host A - Router R1 <-> Router R2 - Host B

If host A need a route to host B, the gateway must be Router R1, *not* 
R2. In fact, R1 and R2 know each other as they are directly connected. 
More, in the case you only have one router for a subnet, it's called the 
default gateway.

It's difficult to give you a precise answer for your problem. I must 
tell you I don't understand you exact network topology: would it be 
possible to give us more info on the networks numbering scheme and the 
different routers?

What I imagine is:
                                            +- Network 172.a.b.c
                                            |
192.168.x.0/24 - [mOn0 A] - VPN Link - [mOn0 B] - Network 172.d.e.f
                                            |
                                            +- Network 172.g.h.i


If it's right, on 192.168.x.0/24, you have mOn0 A as the default 
gateway. But m0n0 A itself use your ISP router as its default gateway. 
And The VPN just creates the static route for m0n0 B's LAN *only*. 
Further networks are not known by m0n0 A.

So, You need to add 3 static routes to the 172. networks on m0n0 A, 
using m0n0 B as the gateway (on its VPN-side interface). Notice: mOn0 B 
should already have routes for all 172. networks.

This is how I see your problem. I may be totally wrong... Let me know.

-- Vincent