I've written extensively on this subject for SearchWin2000.com and for other online sites as well (InformIT.com for one, and GoCertify.com for another). Most experts including myself believe MS won't retire/obsolete the Win2k exams until the next server platform is ready for prime time. Other more informed Windows insiders (like Paul Thurrow) believe that this won't happen until 2006 or 2007. Thus, it seems pretty safe to stick with Windows 2000 certs for at least the next 2-3 years. Plus, you can upgrade an MCSA or MCSE from Win2k to Win2k3 by taking either one (MCSA) or two (MCSE) upgrade exams later, so why worry?
Bottom line: If you wait for Win2k exams to expire, you'll wait a pretty long time. Go ahead and tackle Win2k stuff now, and then upgrade later.
This was first published in October 2003