OKPeery
My suggestion would be if you want ONE specific page to operate in ONE specific way, that you assign a class to the unique page you want that will size that entry appropriately. So instead of having
<div id="content">Content</div>
use on your full width unique pages
<div id="content" class="full_width">Content</div>
With the CSS being
.full_width { width: 100%, or 800px, or whatever is relevent; }
Simply attach the class to the content DIV in the pages you want to be sidebarless. Not neccessarily the most elegant solution, but it works =p.
The advantage of attaching a class instead of creating another DIV-id is that i'm guessing you want the content on all the pages to still be styled in the same manner just with a differing widths. If you used another DIV-ID you would have to duplicate the styling code for your current DIV-ID into the new div-ID, and anytime you are duplicating code problems will soon appear.