Multiple network cards

[Mike Harris]

I have two network cards, on built-in to my motherboard, and a PCI one. For 
each I've compiled the drivers as modules. (e100 for the builin, and 8139too 
for the PCI). One is my internal network, and the other connects to the 
internet.
They both work, but the problem is I can't specify which one is eth0 and eth1, 
and occasionally they'll switch. In /etc/modules.conf and /etc/modprobe.conf 
(I'm not sure of the difference of these files) I have the lines:
alias eth0 e100
alias eth1 8139too
This is what I'd like them set up to be. 
Any ideas why it's not listening to me?
Mike Harris