From MS help
To add a
Windows XP computer to your network
You must be logged on to this computer as an administrator to complete this procedure.
Set up your new computer and physically connect it to your home or small office network.
Start the Network Setup Wizard.
If your network uses Internet Connection Sharing (ICS) and the ICS host computer is running Windows XP Home Edition or Windows XP Professional, run the Network Setup Wizard on that computer first.
Follow the instructions on your screen.
Notes
To start the Network Setup Wizard, click Start, point to Settings, click Control Panel, and then double-click Network Setup Wizard.
The Network Setup Wizard is only supported on computers running Windows 98, Windows 98 Second Edition, Windows Millennium Edition, or Windows XP.
Theoretically speaking, this should suffice. But Windows is far from perfect so don't be surprised if you have problems. I had to mess around a little bit after running the wizard to enable file+
printer+Internet sharing on my computers.