I do believe I need MiamiDX (or some TCP/IP-stack) after all. What I am trying to do here, is getting Internet-access (however slow) for the Amiga, through a serial connection to WinXP.
The Amiga I'm using is an A2000. So a Zorro-NIC would be possible. I just can't seem to find one at a reasonable price, so I thought I'd try this to begin with. And if it turns out it's that enjoyable, I can always try getting a NIC later on. (You should find the specs on the Amiga in my profile, it's not by far beefed up as much as your A4000 though). The use I'm picturing for this connection is mainly IRC, and transfer of smaller files (AmiNET should work fine, given the size of Amiga software - when getting files on AmiNET with my present 100Mbit/s-connection it almost feels ridicilous. I'd say 33Kbp/s is more in line with a fully fledged AmiNET-experience

)
But if you could be so kind as to guide me on how to set up WinXP (pro), in order to achieve this. I would be forever grateful. Some help at the MiamiDX-end would be welcome as well, but I need to get at least one end right, before I can start a trial and error procedure in a remotely efficient manner..