Which Flash Player Version

Which flash player version does everyone design for?

I am making a site and have noticed that simple things like alignment and position change with different flash player versions. Should I just publish it for an older version?

Just wondering how others handle this.

Heres my site if you want to look, its not completed, and its for school

http://www-personal.ksu.edu/~smd3333/personal2/home.htm