if you dont understand it then dont install it
copied and pasted from windows update about this SP
This article discusses the Advanced Networking Pack for Windows XP Service Pack 1 (SP1). The Advanced Networking Pack is an add-on for Windows XP SP1 that includes an updated Internet Protocol version 6 (IPv6) networking stack, an IPv6 Internet connection firewall (ICF), and the Microsoft Peer-to-Peer (P2P) networking platform. The optional Windows Peer-to-Peer networking component provides a framework for peer-to-peer programs to communicate directly between computers over Network Address Translation (NAT) devices and over the Internet.
This article contains information about how to install the Advanced Networking Pack for Windows XP and the Windows XP Peer-to-Peer networking component, discusses IPv6 Teredo NAT traversal technology, lists some known issues, and describes how to troubleshoot and resolve these issues.
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Advanced Networking Pack for Windows XP
The Advanced Networking Pack for Windows XP updates IPv6 and installs the Internet connection firewall for IPv6. By default, no ports are automatically opened in the firewall after the update is installed. Use the Advanced Networking Pack for Windows XP if you have software that requires this functionality or if you want to develop custom programs that use the Windows Peer-to-Peer networking infrastructure.