The coming millenium and the year 2000 are meaningless in themselves. Hell, if we had been created with 8 fingers instead of 10, we would be celebrating the fourth millenium in 48 years. It's just numbers on an arbitrary calender system on an arbitrary mathematic system--nothing else.
And to answer the question why we started with 01 instead of 00 is because Christianity became the official religion of Rome and they began counting relative to the year of Christ's death sometime later. The people in "year 1" didn't even know they were in "year 1" so-to-speak. That happenned sometime later.
Hell, there is more than 1 calender on this planet and it's not even the second millenium on those, either.
So we're not going to die in 3 days nor will we be flying our cars to work.