Entire site is off center on a particular computer
 

This is a bit strange. My site looks fine on my home computers (4 Macs) and on my PC at work. However when I bring it up on my Mac at work, everything is flowing off the right side of the page. I have to believe that it is doing this on some other people's computers. I'v had a number of friends check it for me and it looks fine on theirs. I am attached a screen shot of it here.

I have tried changing the display mode to 1280 by 960, nothing seems to help. My heades is 1300 pixels wide, could this be the problem?

www.womenandadversity.com

thanks so much
Evalee