Switching between two networks

My friend has a laptop he needs to use at two different companies, so he needs to be able to switch between 2 different networks (both using tcp/ip). How can that be best handled? Someone mentioned loading a netswitcher program, but it is not 2000 compatible. Can that be handled with multiple hardware profiles, or does he need multiple nics? Obviously I am not very knowledgeable on the subject, so any detail you can provide on the process (or info on where to find the details) would be greatly appreciated.