@Olympian1010 This time I agree with facts given by @Monzanator (while I don't like the fact he mentions most of Americans being stupid, no matter what I think about it myself).
As there was no year 0, the first century was 1-100. The current century lasts from 1/1/2001 (thank God, it doesn't matter if you read it the logical or the American way of dd/mm ).
However, talking about decades... well, I think these are not as commonly used by historians as centuries, thus these opinions might differ. For example, in most music channels you'll hear about the music of 60s, 70s, 80s.. that would be funny to call music from year 1990 the 80s.