I need to know the exact make and model of your card, unless you are sure of what module you need to load. Also, is this a generic redhat kernel or did you build it yourself?
I believe that RH 9.0 uses grub, and starts be default in runlevel 5. So, lets do the following:
From Redhat manual-
Hopefully it boots. If not, you will have to boot from the first redhat disk, and use linux rescue.
Select Red Hat Linux with the version of the kernel that you wish to boot and type e for edit. You will be presented with a list of items in the configuration file for the title you just selected.
Select the line that starts with kernel and type e to edit the line.
Go to the end of the line and type single as a separate word (press the [Spacebar] and then type single). Press [Enter] to exit edit mode.
You can now use modprobe to try and load your ethernet module. If it can't load, it will tell you why, and you should post that up here.