To configure an ethernet card in Linux, you need to enable it in the kernel. Then the kernel will detect your ethernet card if it is at a common IO port. But it will stop there, and will never check if you have 2 ethernet cards.
The trick is to tell the ethernet driver that there are 2 cards in the system. The following line will tell the kernel that there is an ethernet card at IRQ 10 and IO 0x300, and another one at IRQ 9 and IO 0x340:
ether=10,0x300,eth0 ether=9,0x340,eth1
You can add that line on bootup at the "boot:" prompt, or in the /etc/lilo.conf file. Don't forget to run:
lilo
That will reload the lilo.conf file and enable changes.

configure 2 ethernet cards in linux, kernal errors , linux tweaks