After the fun Microsoft had with Slammer a change was made:
SQL 2000a does exist and is the current version. SQL 2000a is basically the original disk of SQL 2000 with one DLL replaced to protect against getting the Slammer worm. Windows Server 2003 actually has a check for this particular patch (hence the need for SQL SP3a or higher requirement) and disables network access for SQL until it is in place. That is why we have to do the named pipe alias (see http://msmvps.com/clustering/archive/2005/10/19/71580.aspx) for clustered non-default instance installs on Windows Server 2003. Windows Server 2003 doesn’t like installing the original version and prefers SQL 2000a. The easy way to tell is that one or more of the folders in the root of the SQL 2000 CD are now show a date in 2003 instead of in 2000.
Any version downloaded today via MSDN or any of the licensing fulfillment
programs will be SQL 2000a. If you have an older version, contact
whomever you purchased the license from to obtain a new media kit. This has been the case for a few years now, so don’t panic.
Thanks to Geoff N. Hiten a true Microsoft SQL Server MVP for cluing in about all this!