Y2K was an important year for many reasons. First was the belief that many computers were going to stop working since they worked on the notion that last two digits stood for the current year in 19xx. Since there would now be 2 zeros in the last spot, a lot of computer were going to ready 1900 instead of 2000. This was causing a lot of panic about vast areas shutting down due to this error.
Another reason is dependent on what you believe. The year 2000 could either be the first year of the new millennium, or the last year of the current millennium. While everyone has views which one is correct, in reality, both are valid depending on the viewpoint.
If you were to count to 100, you’d start at 1, then end at 100. If you wanted to count another 100, you’d continue with 101, then end at 200. It would be the same with counting a thousand years. Start at 1, and end at 1000. What this would mean is that the year 2000 belongs to the millennial range 1001 – 2000.
An alternate viewpoint is viewing the years as groupings. When you say the 70’s, the range ends up being ’70 to ’79. When you move on to the 80’s, you start with 80. Same could be said with millenniums. Start at 1000 and end at 1999. Then start again with 2000 and one day ending with 2999.
There really is no right answer to this. You can have fun, however, and take the opposite side of whomever you discuss this with. Whatever the case, make 2000 a good year, because whether you look at it as the last or first year of a millennium, you can make it be a good year.