If you are using a braodband router join the Amiga1 to the router or directly to the modem.
If you have been using the modem with a router directly to another computer you will have to power down the modem so the mac address it picks up will be the Amiga1's
Simplest way is to reinstall debian, that way you can set you apt sources to ftp at the same time
You've already got your HD partititioned so:
Interrupt the boot sequence
Insert your debian CD
ide reset
diskboot 500000 1:0 assuming cd-rom is primary slave.
reformat swap partiton etc.
when asked to configure DCHP network, answer yes.
When asked about apt sources, dont select CDROM, use ftp, then select uk or us debian site from the list.
When asked for another apt sources select no.
Your Ethernet will now be working and you'll have the latest stable distro from the net as well.
The rest of the install is the same as the guide eyetech would have shipped to you.