SQL Server stores most of its metadata in system tables in the installed databases. However, SQL Server stores some configuration settings—such as login authentication mode, shortcuts to SQL Server utilities, and so on—in the registry. If SQL Server's registry information is damaged, SQL Server might not start. Make sure you're prepared for this scenario by knowing how to rebuild the registry.
Registry rebuild works differently in SQL Server 2000 than it does in SQL Server 7.0. In SQL Server 7.0, a utility called regrebld.exe backs up SQL Server's registry settings as five .rbk (registry backup) files when you use it with the backup option in the \MSSQL7\Binn folder. The installation program runs the utility upon completion. In a registry-corruption scenario, you could run the Regrebld utility with the -restore option and restore the registry settings that the installation program saved. You could also perform a registry backup by running the utility yourself with the -backup option after editing the registry, but first you have to remove the .rbk files from the \MSSQL7\Binn folder or back up to an alternate location.
SQL Server 2000 has a different procedure for rebuilding the registry. You start the setupsql.exe program, choose Advanced Options in the Installation Selection dialog box, then choose Registry Rebuild. This option doesn't use an existing backup. Instead, it walks you through a set of dialog boxes similar to the ones you walk through when performing a standard SQL Server 2000 installation, then it uses the information you supply to reconstruct the registry settings. Besides reconstructing the registry settings, the registry rebuild option also reinstalls Microsoft Data Access Components (MDAC) and Microsoft Distributed Transaction Coordinator (MS DTC). Note, however, that you must provide exactly the same information you supplied when you installed SQL Server initially. If you can't remember the original choices you made, you need to uninstall and reinstall SQL Server. I suggest making screenshots of the installation dialog boxes and printing them when you're installing SQL Server so that you won't have to memorize the information. Alternatively, you can write down the options as you choose them, but do make an effort to save the settings when you install your server so that you won't have any regrets if your registry becomes corrupted.