A. If you change the NT name of a server and want to change SQL Server 6.5 or below to match it then do :-
sp_addserver <newname>, local
In addition, if you use the IPX/SPX netlib for SQL Server connectivity you must also run the SQL Setup, choose the option to change the network support, and fix the server name in there too.
With SQL 7.0 you will need to re-run setup to reset the server name. Setup will detect the name conflict, resolve it, and then finish.