Sorry to break this one on you American folks, but it was a New Zealander, Richard Pearse that was the first man to fly a powered aircraft.
He flew on 31 March 2003, a full 8 months before the Wright brothers flew at Kittyhawk. :o
I think it only fair that Microsoft include his aircraft, and give him the recognition he deserves in FS2004.
For further reading:
http://www.nzedge.com/heroes/pearse.html