Installing SQL Server 2000 x86 Enterprise on Windows 2003 x64
Yes, SQL Server 2000 x86 can use AWE to buffer data pages above the 4GB limit. See How to configure SQL Server to use more than 2 GB of physical memory:


  sp_configure 'show advanced options', 1
  RECONFIGURE
  GO
  sp_configure 'awe enabled', 1
  RECONFIGURE
  GO
  sp_configure 'max server memory', ...
  RECONFIGURE
  GO


The article also explains how to enable /PAE in boot.ini, but if your OS is amd64 already you don't need it since the OS can already see the entire memory. So all you need is to enable AWE on the x86 SQL Server 2000 instance.