Thanks MaxReboot for this interesting article find..
HOPELESS OPTIMISM must be a fundamental part of human nature, because we want to believe that new operating systems truly represent an improvement on their predecessors. It's easy to point to certain features in a new OS as examples of progress, but end-users often find that a new OS performs like molasses compared to the version they were using. As a result, CTOs wanting to capitalize on the benefits of a new OS may find that new hardware investments are necessary -- and expensive -- requirements.
Unfortunately, Microsoft's Windows XP appears to be maintaining that tradition, as indicated by results of independent testing performed by CSA Research and confirmed by our work in the InfoWorld Test Center. Our tests of the multitasking capabilities of Windows XP and Windows 2000 demonstrated that under the same heavy load on identical hardware, Windows 2000 significantly outperformed Windows XP. In the most extreme scenario, our Windows XP system took nearly twice as long to complete a workload as did the Windows 2000 client.