Use a body class. So set a body class for each page then just call it in the CSS.
Example:
Homepage
HTML Code:
<body class="home">
<div id="container">
<!--Content-->
</div>
</body>
Then in the CSS:
Code:
body.home #container{
width:960px;
margin:0 auto;
...
}
Another Page would be
HTML Code:
<body class="about">
<div id="container">
<!--Content-->
</div>
</body>
CSS:
Code:
body.about#container{
width:460px;
margin:0 auto;
...
}
EDIT: I also dont understand why you are changing the width of the body? It would be more accessible and usable surely if you left it so it could be a bit more responsive???