SQL2000 - Change Server Name & Instance Name

Change the computer name, and reboot the server.
Run following command to change the server name in sysservers system table:

sp_dropserver old_name

GO

sp_addserver new_name, local

GO

To change the server instance's name:

sp_dropserver old_servername\instancename

GO

sp_addserver new_servername\instancename, local

GO