Since they are pushing 100 years into March 2003, it doesn't sound like there will be any big celebration at WDW in 2003. If there were, 100 years would be eating into it. As long as the celebrations are working, i.e. bringing guests in, we'll still see them, probably with a year in between. The Millineum Celebration ended 1/1/01, with 100 years scheduled for October.
This is just a guess, but I think Disney will probably try to alternate celebrations/events between WDW and DLResort.
2000 - Millineum Celebration at WDW
2001 - Opening of DCA/DD at DLResort.
2002 - 100 years at WDW.
2003 - Mickey's 75th at DLResort (Just a guess on my part, but I can't believe Disney would ignore this event, and frankly I would be disappointed if they did)
2004 - Something at WDW?
2005 - DL's 50th anniversary at DLResort.
Again, I have no inside info on this, its just my thoughts on what I think would work best.