moral of this story: track your mac addresses ... pull one card, boot the system, note the mac address ... then insert second card, boot again, note the second mac address, and the mapping of device names (ethX) to mac address.
the way that eth0 and eth1 are assigned to the NICs depends on the kernel (2.6 vs earlier) and module setup and PCI bus.
if you are using an up to date kernel, you can use udev to assign ethX to a specific MAC address.
this is not so simple, even Dell has a white paper about it: http://linux.dell.com/files/whitepapers/nic-enum-whitepaper-v4.pdf
Les