Select @@version on our 64-bit server results in the following
Microsoft SQL Server 2000 - 8.00.760 (Intel IA-64)
Feb 6 2003 16:07:24
Copyright (c) 1988-2003 Microsoft Corporation
Enterprise Edition (64-bit) on Windows NT 5.2 (Build 3790: )
If you don't see a 64-bit tag on yours then you're not using the 64-bit version
The difference between the 2, good questions, the main benefit of the 64-bit version allows much more memory to be addressable by SQL server no need to enable AWE memory. They also cost a hell of a lot more
We've been using ours for the last 6 months and the performance is much better than we initially expected it to be.