Accessing web using both home broadband and office LAN

I have been issued with a Dell notebook. I connect the notebook to my office’s LAN via a fixed IP. HOwever, I access the office’s network using my own broadband service. As a result, I always need to re-key in the office IP address after setting TCP/IP to obtain IP automatically when I use the same notebook at home. How can I set the TCP/IP to a fixed IP and to also obtain IP automatically?