So trying to sort this out, it's just making my brain hurt.
Working on my website (www.alincgov.com), and although I have specified a page width of 900px, the width of the page varies from one page to the next. For example, the "Home" page and "Contracts" page are the same width, while the other three pages (Partners, About, Contact Us) are another width. I tried in three different browsers (IE, Chrome, Firefox) and it appears in all of them.
I can't find any correlation between this width issue and the template in use - for example, Home and Partners are the same template (but render different widths), and Contracts and Contact us use the same template (again, show up as different widths).
Any help would be greatly appreciated.