/etc/modules.conf still exist.
Well, in the older days, you can pass arguments through lilo at boot-time to the kernel to assign eth0 and eth1 to which every NIC you like. Right now I can think of a few "tricks" BUT I have not tested them.
quite sure it will work, not very safe)
Assign the onboard NIC IRQ_no to a bigger no for example 12/13. Before you do this, check what is your current IRQ mapped you can use lspci to check that. So that you do not assign a comflicting IRQ (shouldn't be a problem anymore since kernel can cope with share IRQ).
Edited: Safest is to swap the IRQ of realtech NIC to nforce and vice-versa. Do this in BIOS.
Trick 2: (more probable, not sure it will work)
Have both the NIC drivers compiled as modules.
Edit /etc/rc.d/rc.modules so that modprobe for the realtech NIC comes before the nforce NIC.
I am saying that this may not work since the kernel nowadays seems to be not relying on modules startup script fully.
Trick 3: (it is abit outdated, never got it working, but you may be able to)
Use the lilo to pass arguments to the kernel. Read Ethernet-Howto from www.tldp.org
; the section where you can set up two-nics.
Trick 4: (SURE WORKS, with some pain)
Just live with it! It is seemless anyway, you won't need to know eth1 or eth0 when using the comp normally, only when you are doing configuration and maintance, you need to tweak your mind.