Forum Width Question

[jbl7979]

I want to modify the width of my forums, but I only want it to modify the width of the posts and/or the list of forum categories. I do not want it to change the width of the portal page. I searched around and found that if I modify the following piece of code in overall_header.tpl:

Line number On/Off | Expand/Contract | Select all

<added><div><end>  <table>

And change that to width="x" with x being what I want, that it makes the changes to the pages I want, but it also affects the portal page. Anyway I can do this without it having the portal page shrink?