You can download it here (a 1,247KB download) and read more about it in MSKB article 817778. Briefly, it includes IPV6 support, including a firewall, and support for the peer-to-peer networking components (peer-to-peer networking name resolution, peer-to-peer networking graphing, peer-to-peer networking grouping and the peer-to-peer networking identity manager). If you’re interested, read the MSKB article.