Ubuntu Networking :: Manual Update Of Ifconfig?

To get internet access on my second computer I have to follow the manual routine detailed below:

sudo ifconfig eth0 down
sudo ifconfig eth0 hw ether ..........
sudo ifconfig eth0 up
sudo ifconfig eth0 ....... netmask ........ broadcast ........
sudo route add default gw .........

where the various ........ represent the relevant addresses. This is necessary because my ISP only recognizes one computer - my first one. The above works fine, I simply copy and paste the above from a text document, but I would like to know which files I can alter/create so that all the above is achieved automatically when I boot my second computer.