
xx2: This is most probably because you have a -tag that is a certain width. Create a page template for the forum and add a class to that div and change it via CSS.
If you wrapper div for the content is;
YOUR STUFF
Change it (in your new page template…) to..
YOUR STUFF
Then refer it in the css with an ancestor id to overwrite the #content formatting IF it has the class .wide:
#container #content.wide {width:auto;}
- OR-
#container .wide {width:auto;}
- OR -
#container .wide {width:100%;}
If it looks bad, remember to set appropiate padding or margin on the class .wide.