To add a little more to this, I'd like to make it a fixed size of 800px wide, here is the skin.htm if that is helpful:

<table width="100%" height="100%" border="0" cellspacing="0" cellpadding="0" ID="Table2">
    <tr>
        <td height="44" background="top_tile.gif" align="center" colspan="3">
            <table width="98%" height="44" border="0" align="center" cellpadding="0" cellspacing="0" ID="Table3">
                <tr>
                    <td width="100%" height="44">[CURRENTDATE]&nbsp;&nbsp;&nbsp;[BREADCRUMB]</td>
                    <td width="100%" height="44" align="right">[LOGIN]</td>           
                </tr>
            </table>
        </td>
    </tr>
    <tr>
        <td height="93" colspan="3" class="SkinImage">[LOGO]</td>
    </tr>
    <tr>
        <td width="3%" height="28" background="menu_tile.gif" align="left"></td>
        <td width="55%" height="28" background="menu_tile.gif" align="left">
            <table border="0" cellpadding="0" cellspacing="0" height="28" ID="Table1">
                <tr>
                
          <td>[MENU]</td>
                </tr>
            </table>
        </td>
        <td width="42%" height="28" background="menu_tile.gif" align="right">[USER]&nbsp;&nbsp;</td>
    </tr>
    <tr>
        <td bgcolor="3E6DA1" colspan="3" height="100%">
            <TABLE WIDTH="100%" HEIGHT="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" bgcolor="white" ID="Table4">
                <TR>
                    <TD id="LeftPane" runat="server" WIDTH="200" visible="false" VALIGN="TOP" height="100%"></TD>
                    <TD id="ContentPane" runat="server" HEIGHT="100%" visible="true" VALIGN="TOP"></TD>
                    <TD id="RightPane" runat="server" WIDTH="200" visible="false" VALIGN="TOP" height="100%"></TD>
                </TR>
            </TABLE>
        </td>
    </tr>
    <tr>
        <td height="25" background="footer.gif" bgcolor="#3E6DA1" align="left" colspan="2" valign="middle">&nbsp;&nbsp;[COPYRIGHT]</td>
        <td width="42%" height="25" background="footer.gif" bgcolor="#3E6DA1" align="right" valign="middle">[TERMS]&nbsp;&nbsp;[PRIVACY]&nbsp;&nbsp;</td>
    </tr>
</table>

Strauss,

Get rid of the width="100%" from the parent table and give it a CSS class.

<table class="ContentWrapper">

</table> 

Put this in your skin.css file:

.ContentWrapper {width: your_fixed_width;}

Inline CSS is a bad practice and it will cause you more headache in the future.