Here is the link for MS SQL Server 2000 sp4 download

http://www.microsoft.com/downloads/details.aspx?FamilyId=8E2DFC8D-C20E-4446-99A9-B7F0213F8BC5&displaylang=en

You will need to install the Database Components (Download file: SQL2000-KB884525-SP4-x86.EXE)

If you have Analysis Services installed along with SQL Server, then also install Analysis Services Components (Download file: SQL2000.AS-KB884525-SP4-x86.EXE):

These patches are assuming that you have a 32bit system and not 64