The scanner would have firewire 400 port, and a new iMac would have a Firewire 800 port. This is likely the difference that Blair Seitz means.
You need a Firewire cable, with FW400 on one end, and FW800 on the other end. This cable should be available at any shop where you purchase a new Mac...
The scanner would originally have come with a USB cable, according to Epson, and there should be no problem with using that connection to your iMac.