http://support.microsoft.com/kb/914440

This tool is available to help you identify and fix connection problems. These connection problems may occur with computers on a home network that connect to the Internet by using a cable modem or by using a digital subscriber line (DSL) modem.

To diagnose network connectivity status, the Network Diagnostics for Windows XP tool analyzes the following tests:

• IP configuration test 
• Default gateway test 
• Winsock test 
• DNS test 
• Firewall test 
• Internet connectivity validation test
• Typically, a support professional will work with you when you run the Network Diagnostics for Windows XP tool to help diagnose network connectivity status.

Most home networks use one of the following methods to access or share a single high-speed Internet connection:

• A stand-alone router 
• A home gateway, such as a cable modem together with a router or a DSL modem together with router 
• A computer that is running Internet Connection Sharing or another form of Network Address Translation (NAT)