Dual IP on one internet card

For Ubuntu do :
$ cd /etc/network/
$ sudo vi interfaces

Then add follow line in:
If your 1st ip config is:

iface eth0 inet static
address 172.xxx.xxx.xxx
netmask 255.255.xxx.xxx
...
auto eth0

Now add 2th ip :

iface eth0:1 inet static
address 192.xxx.xxx.xxx
netmask 255.255.xxx.xxx
auto eth0:1


do:
#sudo /etc/init.d/networking restart