...with 10/100 Ethernet card...
Normally, those are PCI-cards. A normal A4000 doesn't have PCI-slots, in which case a Zorro-card like the XSurf or an Ariadne will work perfectly (I use a XSurf in both my A2000 and A3000). Zorro ethernetcards only come in 10 Mbps, but this will not make any difference in daily use.
Broadband on the Miggy works nicely. FTP, chat, Telnetconnections, e-mail are all fully usable and enjoyable. Browsing is hell (imo), though.