function switchMenuVisibility(menuitem, knob)
{
    var src=knob.firstChild.src;
    // Iterate through all TDs in 'leftmenu' table
    var table = document.getElementById('leftmenu');    
    for(var i = 0; i < table.rows.length; i++)
    {
        if(table.rows[i].id.indexOf('menu'+menuitem+'_') > -1)
        {
            if(table.rows[i].style.display=='none')
            {   
                table.rows[i].style.display='';
                //knob.firstChild.src=src.replace('plus.gif','minus.gif');
                knob.innerHTML='<img border=\"no\" align=\"bottom\" src=\"/images/minus.png\" />';
            }else{
                table.rows[i].style.display='none';  
                //knob.firstChild.src=src.replace('minus.gif','plus.gif');
                knob.innerHTML='<img border=\"no\" align=\"bottom\" src=\"/images/plus1.png\" />';
            }
        }
    }    
}