MS KB820342 will impact P2P users 1- Windows XP-based machines are capable of bootstrapping into a link local cloud consisting of computers that are running Windows Vista. 2- A Windows Vista-based computer cannot bootstrap into a link local cloud that only consists of Windows XP machines that are running PNRP v2.0. This behavior occurs because PNRP bootstrapping uses the Simple Service Discovery Protocol (SSDP) over IPv6 in Windows Vista and IPv4 in Windows XP. Note PNRP version 2.0 is not backward-compatible with earlier versions of PNRP. If you install this update, you cannot use programs that use the updated version of PNRP to communicate with programs that use earlier versions of PNRP. Also, Windows XP does not let applications use the getaddrinfo() Windows Sockets function to resolve PNRP names that are encoded as fully qualified domain names.