I see that there's Windows 2000 and SQL Server 2000 involved. Then you should read this blog, and even more so the links included: http://blogs.msdn.com/b/joaol/archive/2008/02/05/sql-server-2000-64-bits-versus-sql-server-2000-32-bits-memory-management.aspx
That depends on which version and edition of SQL Server you are running. For SQL Server 2005, there's a post on the Microsoft CSS SQL team blog: http://blogs.msdn.com/b/psssql/archive/2008/04/05/sql-server-2005-memory-limits-and-related-questions.aspx
As you can see in that article, it also depends on what Operating System version and edition you are using.
You can read further about memory limits for SQL Server 2008 R2 here: [http://msdn.microsoft.com/en-us/library/ms178067.aspx]
So.. I'm sorry to say, but the answer to your question is: It depends :): http://msdn.microsoft.com/en-us/library/ms178067.aspx
It depends on the exact version of Windows and SQL... Assuming you're running SQL Server 2008, then [this page] lists the minimum, recommended, and maximums available to you.: http://msdn.microsoft.com/en-us/library/ms143506.aspx