This is what my Win7 "Help" screen says about internet connection sharing (ICS):
Enabling ICS
To enable ICS, on your host computer:
Click to open Network Connections.
Right-click the connection that you want to share, and then click Properties. Administrator permission required If you are prompted for an administrator password or confirmation, type the password or provide confirmation.
Click the Sharing tab, and then select the Allow other network users to connect through this computer's Internet connection check box.
Notes
The Sharing tab won't be available if you have only one network connection.
You can choose whether to select the Allow other network users to control or disable the shared Internet connection check box.
Optionally, to allow other network users to use services running on your network, click Settings, and then select the services you want to allow.
When you enable ICS, your local area network (LAN) connection gets a new static IP address and configuration, so you'll need to reestablish any TCP/IP connections between your host computer and the other network computers.
To test your network and Internet connection, see if you can share files between computers and make sure each computer can reach a website.
I believe that is also how I did it on my WinXP laptop. When they say "click to open network connections" that is in the Control Panel.