Im using 2000pro service pack4, here you can see that intel does not recommend using hyper threading with 2000pro:<A HREF="http://www.intel.com/support/platform/ht/os.htm?iid=ipp_htm+os&" target="_new">http://www.intel.com/support/platform/ht/os.htm?iid=ipp_htm+os&</A>Edit: And hyperthreading does work with 2000pro.