After you have ordered an extra IP Address through the cPanel, you will need to assign the new IP to the NIC in VPS.
After you have ordered an extra IP Address through the control panel (see http://www.vpsblocks.com.au/support/Knowledgebase/Article/View/18/0/how-do-i-add-another-ip-address) you will need to assign the new IP to the NIC in your VPS.
The network config file you need to edit is at: /etc/network/interfaces
auto eth2iface eth2 inet staticaddress 192.168.210.100netmask 255.255.255.0gateway 192.168.210.1
Adding more IP addresses to those interfaces is as simple as creating an alias, done by duplicating the information for the initial interface and appending a colon followed by 0,1,2,3,etc according to how many aliases are needed, minus the gateway (the initial IPs gateway will be used):
auto eth2:0iface eth2:0 inet staticaddress 192.168.210.101netmask 255.255.255.0
auto eth2:1iface eth2:1 inet staticaddress 192.168.210.102netmask 255.255.255.0
When finished run: /etc/init.d/networking restart
This will activate the changes and make the new IP address live.