You will find good answers to all your questions on the Microsoft Web site--yes, it is really true! -in the MCSE FAQ. Be sure to scroll toward the bottom of that document and look for the heading "Frequently Asked Questions about Windows XP Professional and Whistler Server Exams." My opinion is that if you are serious about obtaining an MCSE, you should charge ahead and finish up on Win2k topics as soon as you can. As you'll see in the FAQ, Microsoft plans to let MCSEs mix and match XP/Whistler Server exams with Win2k exams to their hearts' content anyway.
This was first published in June 2001