Oh, but he is right, actually! XP /is/ much quicker to start up than
w2k. It also requires much less resources after the startup. So on the
same machine the user will get a feeling that it is much slower running
under Windows 2000 that if he did the same things under Windows XP.
I actually see this often myself, because we have an older test machine
here with multiple boot, including both of the above alternatives. Both
OS are cleanly installed/reinstalled except for eTrust antivirus which
is added, so I'm pretty sure it's due to OS differences rather than
anything else.
That doesn't answer the answer /why/ it is so, though...