td widths, not working?

So I have this code here:

<table>
    <tr>
        <td width="200px" valign="top">
            <div class="left_menu">
                <div class="menu_item">
                    <a href="#">Home</a>
                </div>
            </div>
        </td>
        <td width="1000px" valign="top">Content</td>
    </tr>
</table>

with the CSS

.left_menu {
    background: none repeat scroll 0 0 #333333;
    border-radius: 5px 5px 5px 5px;
    font-family: Arial,Helvetica,sans-serif;
    font-size: 12px;
    font-weight: bold;
    padding: 5px;
}

.menu_item {
    background: none repeat scroll 0 0 #CCCCCC;
    border-bottom: 1px solid #999999;
    border-radius: 5px 5px 5px 5px;
    border-top: 1px solid #FFFFCC;
    cursor: pointer;
    padding: 5px;
}

It works fine on my browser and I have tested it in every browser both mac and PC, but someone is complaining that the td with the width of 200 keeps changing width. I have no idea what he is talking about. Does anyone know why he or she is seeing the width change on the td?

It should be:

<td width="200">

or

<td style="width: 200px">

Note that if your cell contains some content that doesn't fit into the 200px (like somelongwordwithoutanyspaces), the cell will stretch nevertheless, unless your CSS contains table-layout: fixed for the table.

EDIT

As kristina childs noted on her answer, you should avoid both the width attribute and using inline CSS (with the style attribute). It's a good practice to separate style and structure as much as possible.

Width and/or height in tables are not standard anymore; as Ianzz says, they are deprecated. Instead the best way to do this is to have a block element inside your table cell that will hold the cell open to your desired size:

<table>
    <tr>
        <td valign="top">
            <div class="left_menu">
                <div class="menu_item">
                    <a href="#">Home</a>
                </div>
            </div>
        </td>
        <td valign="top" class="content">Content</td>
    </tr>
</table>

CSS

.content {
    width: 1000px;
}

.left_menu {
    background: none repeat scroll 0 0 #333333;
    border-radius: 5px 5px 5px 5px;
    font-family: Arial,Helvetica,sans-serif;
    font-size: 12px;
    font-weight: bold;
    padding: 5px;
    width: 200px;
}

.menu_item {
    background: none repeat scroll 0 0 #CCCCCC;
    border-bottom: 1px solid #999999;
    border-radius: 5px 5px 5px 5px;
    border-top: 1px solid #FFFFCC;
    cursor: pointer;
    padding: 5px;
}

 <table style="table-layout:fixed;">

This will force the styled width <td>. If the text overfills it, it will overlap the other <td> text. So try using media queries.