Creating an additonal IP in Debian

It's extremely simple, but there are two things you need to note
1) make sure you have it set in auto
2) The ip details themselves

The file is at /etc/network/interfaces

after editing the file, restart the network /etc/init.d/networking restart

An example of auto..
auto lo eth0 eth0:1 eth0:2 eth0:3 eth1

iface eth0 inet static
        address x.x.x.x
        netmask x.x.x.x
        network x.x.x.x
        broadcast x.x.x.x
        gateway x.x.x.x
        # dns-* options are implemented by the resolvconf package, if installed
        dns-nameservers x.x.x.x
        dns-search XX_name.com.local
iface eth0:1 inet static
        address x.x.x.x
        netmask x.x.x.x