Both width and max-width both works in Opera, assuming the rest is ok as well. For example
#head
{
margin: 0 auto;
border-width: 1px;
border-color: black;
border-style: solid;
/* using either width or max-width works just fine */
width: 966px;
}
</style>
</head>
<body>
<div id="head">
This is #head. It is centered left-right due to auto margins, and has a 966px
wide box, as shown by the border.
</div>
But if the rest isn't correct, and also not included in the original post, there's no telling what would or should happen. Among other things id could be missing on misspelt, or invalid html code could mean the browser force closes the element before the author intended. And there are probably a hundred or so other possible errors.
For example using the same stylesheet with garbage html
<p id="head">
<p id="not_head" style="border: 1px solid red;">
This is (not) #head
</p>
</p>
This would show a 0x966px paragraph with black border followed by a 100% wide paragraph with text "This is (not) #head" and a red border, since it translates into this html
<p id="head"></p>
<p id="not_head" style="border: 1px solid red;">
This is #head (not...)
</p>