I have an A1200 and I was given for free a 3Com EtherLink card model 3c589c :-D ! I asked the same thing and people said to me that it is a pain in the arse to set your Amiga to access a LAN.
In my work we have a LAN and plenty of windoze/linux gurus. I decided to surprise them by setting up my miggy to access the LAN. I downloaded the 3c589 drivers from aminet and I have Miami installed. I was told that all I will do with the current software will be to be able to ping the migy and nothing else :-x ! I wonder if this is true, or Miami will allow me to access the web through my miggy.