No x64 (AMD64) version of Windows 2000 ever existed. AMD64 CPU's didn't debut until 2003 and XP x64 was based off the work done on 64-bit Server 2003 for Intel's 64-bit Itanium chips
There was a brief period of Alpha machines that ran 64-bit CPU's that had early "Whistler" builds but nothing ever released to the public
There was a brief period of Alpha machines that ran 64-bit CPU's that had early "Whistler" builds but nothing ever released to the public