That depends mainly on what software you use. Testing shows 10-20%
improvement in thruput for software that is written to take advantage of
HT or dual processors. Windows 2000 will see HT proccessors as dual
CPU's and will sometimes provide marginal improvement over non-HT
processors. You will be best served by doing a bit of reading about HT
and how different software packages run on those CPU's and then decide
about switching operating systems.