I'm going to document it here since I couldn't find this information anywhere 
else and I was able to stumble upon this simple solution.

If you are using LinuxPPC R4, simply do the following:

cd /etc/sysconfig/network-scripts
cp ifcfg-eth0 ifcfg-eth0:1

Then edit the ifcfg-eth0:1 file and change the IP address to the new one.
If you want to add another IP address, change the :1 to be :2 and so on. 
When you reboot the machine, the new IP address will take effect. You can 
have it take effect right away by typing:

ifup ifcfg-eth0:1

I hope that helps someone.

-jon stevens
jon@clearink.com

I had some trouble when I tried this initially; you may also need to change the DEVICE line in ifcfg-eth0:1 (for instance) to reflect eth0:1 instead of just eth0.

To do this under SuSE Linux 7.0 for PPC:

As root, open /etc/modules.conf in a text editor.
Look for the line(s) added by YAST for the ethernet device (usually "eth0"). 
The lines were at the very end on my installation.

For example, mine says:

        alias eth0 mace

(Yours might have something other than "mace" depending on what your 
networking hardware is.)

Next, add as many of the following lines as you need for all your IP addresses, 
incrementing the number after the colon for each one (and if yours doesn't say
"mace", replace "mace" with what yours already says).

        alias eth0:1 mace
        alias eth0:2 mace
        alias eth0:3 mace
etc...

Save it, then launch YAST.

Go to System Admin > Network > Base Network Config

Add your first IP to device eth0 (as if nothing unusual is happening).

For the rest, use the <Enter other device> option, and use the
aliases you created in the modules.conf file (eth0:1, eth0:2, etc).

Hit F10 to commit the changes, and then try pinging the addresses from another 
machine to test. 

Disclaimer: I have no idea if this is the "correct" or best way to do it! But
it worked.