I've done it with MiamiDX. My Amiga 1200 had pcmcia ethernet card (conected via switch and cable modem to internet) and serial connection with A4000. with the help of people here, I have even managed to run smbfs and share directories, surf, etc.. with A4000. the most important thing was to setup SOCKS server at A1200 (in my case, it may be a4000 in your). I can't remember other details right now, but could provide you with config files in case you wanna try Miami DX. BTW, I thing DX version is reqired for socks (IIRC).
