This seems like an easy one but I cannot figure it out, when I make my left sided menu disappear and there is no other content in the left column, the left column refuses to disappear so we can use the whole width of the content area, it is an artisteer generated skin, here is the code:

<div class="art-content-layout-row">
<asp:Panel ID="divLeft" runat="server" CssClass="art-layout-cell art-sidebar1 leftside"
Visible="True" SkinID="pnlPlain">
<portal:SiteMenu ID="SiteMenu1" runat="server" UseTreeView="true" HideMenuOnSiteMap="false"
SuppressImages="true" ></portal:SiteMenu>
<asp:ContentPlaceHolder ID="leftContent" runat="server">
</asp:ContentPlaceHolder>
</asp:Panel>
<asp:Panel ID="divCenter" runat="server" Visible="True" CssClass="center-rightandleftmargins"
SkinID="pnlPlain">
<portal:Breadcrumbs ID="Breadcrumbs" runat="server"></portal:Breadcrumbs>
<portal:ChildPageMenu ID="ChildPageMenu" runat="server" CssClass="txtnormal"></portal:ChildPageMenu>
<a id="startcontent"></a>
<asp:ContentPlaceHolder ID="mainContent" runat="server">
</asp:ContentPlaceHolder>
</asp:Panel>
<asp:Panel ID="divRight" runat="server" Visible="True" CssClass="art-layout-cell art-sidebar2 rightside"
SkinID="pnlPlain">
<asp:ContentPlaceHolder ID="rightContent" runat="server">
</asp:ContentPlaceHolder>
</asp:Panel>
</div>

The left column refuses  to disappear and outputs like such

<div id="ctl00_divLeft" class="art-layout-cell art-sidebar1 leftside left2column cmszone">

</div>

Any help would be much appreciated.