The most important consideration here is what processor you will be using. 
If you a planning on a new P4 then it will support HT, or hyperthreading, 
which Windows 2000 does not support. HT, makes the processor appear to XP 
like two processors. This is not dual core, but was the first step toward it.

  The result of HT is that you will see two processors under device 
manager, one of which, of course, is virtual, and you will realize around a 
12 percent boost in overall  performance over Windows 2000, when running XP 
PRO with a HT processor.

If, however, you have a AMD setup, then HT will not come into play.

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