I would like an expert (preferably a Microsoft employee)
to comment on the following. It has been successfully
tried and found to work:

================================================== ===
ICS with single Network Card and Incoming Connections
================================================== ===

Scenario:
--------
Computer has
- Single LAN adapter: used to connect to the Internet
- Incoming Connections set up (e.g. direct-cable)

Aim:
---
Share the Internet connection through the LAN
with the clients connecting in through Incoming
Connections.

Problem:
-------
By default, ICS expects the private (or home) network to
be accessible via a LAN (or wireless) network adapter. As
a consequence, when you only have a single network card
which has the Internet connection on it that you are
trying to share, it will not do it.
The other problem is that ICS does NOT recognise Incoming
Connections as a valid home network.

Solution:
--------
This configuration does work on Windwos Server products,
where the MMC configuration for RRAS allows the use of
NAT as one of the protocols (see KB article 310888).
However, on XP (Home or Professional), officially it's
not possible.

The solution entails the (as far as I know) undocumented
use of the NAT service in conjunction with the Routing
and Remote Access service.

1) DISABLE(!!) any occurence of ICS using the Network
Connections in Control Panel.
2) Open a DOS Command Prompt and issue the following
commands in sequence.
3) netsh routing ip nat install
4) netsh routing ip nat add "Local Area Connection" full
5) netsh routing ip nat add Internal private

With the above set up, the same effect will be achieved
as if ICS was enabled on the LAN adapter. The result of
the above commands is remembered even after a reboot.

WARNING: after the above commands have been issued, it
will not be possible any more to use ICS via the Control
Panel!

To restore previous functionality, issue the following
command:
6) netsh routing ip nat uninstall

Explanation:
-----------
The NAT service is formally independent of ICS, although
in Windows XP it's usually the latter that makes use of
it. However, just like in Server products, it is possible
to get the Routing and Remote Access Service to make use
of the NAT Service. The commands detailed above have the
same result on XP as using MMC to configure RRAS on a
Server would do. They simply install NAT as a protocol
for the RRAS Service and configure it.

After the above commands have been issued, NAT will be
bound to the RRAS Service, which is why ICS will not be
able to make use of it. If you attempt to set up ICS via
the Control Panel, you get an interesting error message,
which is clearly intended to be ever shown on a Server
product as it refers to the (in XP non-existent) Routing
and Remote Access Service snap-in.