I was pretty pleased with myself for getting the 486 up and running - although this was pretty short lived when I found that I had no network. I could see that DSL recognised the NIC a DLink DE-220P and started the eth0 service, but I couldn't get a network connection. Even the ADSL modem/router wasn't recognising the box.
Googling on linux and DLink DE-220P showed that this card was supported, good news but not helpful.
After mucking around with the control panel and anything vaguely related to network setup (none of which was any good) I looked in the System Stats button, and the DMESG tab showed that the NIC was being recognised (IRQ5), but also NETDEV WATCHDOG: eth0: transmit timed out.
Googling this message wasn't really returning anything of value - but I did notice a post about this being related to an IRQ conflict, then the penny dropped. I was sure IRQ5 was used by the sound card. As this was redundant in this box I decided to rip it out. The sound card was configured to use IRQ5, so I left it out and restarted the box - problem solved.