Adding Ad Space Next To Forum Main

[kiddo1cnc]

On the Forums Main Page I have edited all the CSS files to make everything in the body to 80%. The remaining 20% on the right hand side I would like ad space which scrolls down the right hand side right next to the forums.





This image should clear up any confusion. I had it perfect in 3.8 but when upgraded to 4.0 this code doesn't work. I went thru all the main forum css files and moved the width for everything to 80%. But how do I use the remaining 20% for ads?

Thanks so much guys!