"NWLink IPX/SPX/NetBIOS Compatible Transport Protocol" is an alternative protocol that can be used to connect computers in a Local Area Network, instead of using TCP/IP. It *CANNOT* be used to connect to the internet which must use TCP/IP.
IPX/SPX can be installed optionally in Windows XP if someone is having problems accessing other computers in a Local Area Network, but it isn't installed by default.
If you do actually have IPX/SPX installed but aren't using it, open the Network Connections folder, highlight one of your network adapters ("Local Area Connection" or "Wireless Network Connection") right click it and select Properties. Highlight the entry for "NWLink IPX/SPX/NetBIOS Compatible Transport Protocol" and click the Uninstall button.