I have my Amiga 1200 connected to ADSL via PCMCIA Network card,Miami and a router, took only minutes to set it up and get it working.
I have my Amiga, wifes laptop and my AmigaOne all connected simultaneously.... which is nice!
I co-wrote a feature in Total Amiga magazine on how to do this. It is in issue 12 which luckily sold out very fast so we have it available to download in PDF format.
Go to
http://www.totalamiga.org then to back issues and you will find it there.
I checked a few moments ago and it looks like the site is down for maintenance (hosted on Sixgirls). So maybe try a little later :-)