catch box free

If you go to freethecube.com/wp you will see that I adjusted the width of the body and the "blog frame" a bit. What I am wanting to do tho is have those two widths float with the width of the browser window. I dont want the side bar to change width, only the body over all and where you read the posts. So what css do I need to change and in what way does it need to change for the over all width and the blog width to float from a sensible minimum to around the body being around 80% the width of the browser? Thx.