Problem with CSS positionning

Hello,

I've designed a website without using any tables, everything is
positioned using CSS, content goes into divs. However I've noticed that
the website looks different across browsers. I would like to know how
to avoid this without having to include a CSS for every browser. Here's
a link to the page
http://www.myexersize.com/biography/

I am using absolute positioning. I am thinking of changing that to
relative.
The website displays quite nicely on IE6

Please advise.