ifconfig eth0 192.0.0.1 ...
ifconfig eth0:1 10.0.0.1 ...
if this is what you are talking about then you can add the script. it has been some time since i touched rh9 but on rhel2.1/3/4 and fc1/2/3 and the scripts are found in /etc/sysconfig/network-scripts/
you should have an ifcfg-eth0 already. copy it to ifcfg-eth0:1 (cp ifcfg-eth0 ifcfg-eth0\:1) and then edit it with the appropriate information being sure to change DEVICE=eth0 to DEVICE=eth0:1
doing this should also allow for if[down|up] eth0:1 to work
...or you could just add your ifconfig for the virtIP to rc.local
hope this helps