1> All time greatest achievement - Internet

2> 20th Century's greatest achievement - The Computer

3> So far the greatest achievement of 21st Century - Hmm I can't think of any...

4> All time worst achievement - Murder

5> 20th Century's worst achievement - Holocaust and the atomic bombings of Hiroshima, and Nagasaki

6> So far the worst achievement of 21st Century - Electing George W. Bush as President.