A firewall is a blocking mechanism that helps to keep intruders out of a network (see Chapter 18 for more information about firewalls).
If you are connecting your Centrino laptop to a private network that is itself connected to the Internet, you are probably already protected by a firewall built in to the network hardware (the router) and do not need to enable a personal firewall.
However, if you are connecting to the Internet directly with your Centrino laptop, for example at a public hotspot, it is a wise precaution to enable the personal firewall software built in to Windows XP. (See Chapter 17, "Protecting Your Mobile Computer," for more information.)
To enable the Windows XP personal firewall, open the Windows Firewall item in the Control Panel. Be sure the On radio button is selected. Finally, click OK to preserve the setting.
Figure 3.27. Enabling the personal firewall software built in to Windows XP helps protect your computer when you are directly connected to the Internet at a public hotspot.
With Windows XP Service Pack 2 (or "SP2" as it is affectionately known), the Windows XP personal firewall is enabled by default. In other words, it will be turned on unless you turn it off. So if you've installed SP2, you don't need to take the steps outlined here to enable the Windows XP personal firewall.