Seriously, isn't it faster and easier to just buy a cheap PCMCIA network card and connect it directly to the router? For the A1200 I mean..
The same goes for the A4000, a second hand network card should be quite cheap.
I know it is not helping your question, which I'm sorry for. I have never tried your approach.
Personally I would buy an external router, which usually has 4 inputs, and connect each computer directly to the router. It's way way easier than your approach. The price of such a router should be less than 100$.
This worked straight away when I tried MiamiDX on my A4000. Just set it up to use DHCP and your online
Routers do help alot with making configuration easier when going online.