My PC (WinXP) has an ADSL connection to internet and is also networked to Amiga (I have two ethernet cards on th PC). I use X-Surf2 on Amiga 4000 with Miami Deluxe and Samba. PC and Amiga can share resources and access them in either direction without problem (no other software is needed on PC). Furthermore I can access internet simultaneously from Amiga and from PC. However I had to install a freeware proxy on the PC (no further harware needed).
Samba configuration is a little bit tricky, but if you follow the docs you should have no problem. You also have to set up the TCP for the Amiga<->PC LAN.
The connection to internet from Amiga is as fast as that on the PC!!! ;-)