To create multiple IPs per Interface in CentOS 5

Create the virtual interface

vi /etc/sysconfig/network-scripts/ifcfg-eth0:0

Populate the file

DEVICE=eth0:0
ONPARENT=yes
IPADDR=10.10.10.10

Bring up the interface

/sbin/ifup eth0:0

The interface will be brought up and down automatically as the parent interface (eth0) changes state.