Using laptop on office LAN and at home o

My boss has a laptop that he uses at work that uses DHCP, for his IP address, to connect to our network. He just had DSL installed at home with a static IP address that he needs to use. What do I need to do, other than keep inputing the IP address for him to be able to log onto his Windows 2000 machine and see his desktop like he sees at work.
To make it more complicated he has access to Roadrunner at another location that he will use every now and then that I will eventually need to put into the above equation.