Router and Messenger revisited

Well, I'm still fighting this problem whilst waiting for some
higher-level Netgear support to help.

Using XP Messenger v5.0. Netgear 834 router, UPnP compatible. One
machine allows me to use Messenger video/audio through the router, but
no other machines on the local network work with audio/video. They all
communicate happily this side of the router. I've downloaded about 2
reams of text from Microsoft and other sites and am slowly reading and
testing. The machine that works is a desktop, all the other XP machines
are laptops, which come and go. I haven't got a second XP desktop
machine, but some of the laptops stay on the network for very long
periods.

Can anyone confirm that it should be possible for any machine at any one
time to be routed through the router. The Microsoft docs seem to
indicate that only one UPnP controlled mapping is possible through this
sort of router, so is it possible that something is not removing itself
properly from the router?

When I look at my Internet Gateway screen and Properties->Settings, I
get the following message:
""The Internet Connection Sharing computer is not configured to let
network users control or disable the shared internet connection. The
setting can be changed in the Advanced properties of the internet
connection sharing computer" .

Could this mean that somewhere I have a machine that still thinks it is
providing ICS for the whole network? Or is it just Microsoft's way of
saying that the router is not configurable?

On some of the machines (eg the one I'm on now) this Internet Gateway
icon comes and goes seemingly at random in the Network Connections
screen. One day it's there, the next day not. What causes this?

Are there any apps that will let me monitor what is happening? I can
look at things like Netstat, but they don't show any obvious differences
between the machine that works and the rest.

Any other guidance or suggestions welcomed. Jonathan? Anyone?
--
Bill Holt