Try opening "My Network Places" Properties.
-- Then select the LAN connection you want to use.
-- Right-click on that connection, select Properties on the drop-down.
-- On the General tab you will find the installed protocols.
-- If you do not see NetBIOS, press the Install button, then select Protocol, then select NWLink IPX/SPX/NetBIOS Compatible Transport Protocol. You'll have to have your XP installation disk to load it.
-- If you do see it installed, it is not working. Uninstall it and restart your computer. After restart, follow the steps above to re-install it.