//If the user submits the form, then hits the back button, the correct element / hidden
//div is forgotten.  This fixes that problem.
function checkHiddenElements()
{
    if (document.the_form.unit_type[0].checked) {
	switchDiv( 'ac_form' );
    }
    else if ( document.the_form.unit_type[1].checked) {
	switchDiv( 'boiler_form' );
    }
    else if ( document.the_form.unit_type[2].checked) {
	switchDiv( 'furnace_form' );
    }
}
function hideAll()
{
    changeObjectVisibility("ac_form","hidden");
    changeObjectVisibility("boiler_form","hidden");
    changeObjectVisibility("furnace_form","hidden");
    changeObjectVisibility("no_js_msg","hidden");
}
function changeObjectVisibility(objectId, newVisibility) {
    // first get the object's stylesheet
    var styleObject = getStyleObject(objectId);

    // then if we find a stylesheet, set its visibility
    // as requested
    //
    if (styleObject) {
	styleObject.visibility = newVisibility;
	return true;
    } else {
	return false;
    }
}
function getStyleObject(objectId) {
    // checkW3C DOM, then MSIE 4, then NN 4.
    //
    if(document.getElementById && document.getElementById(objectId)) {
	return document.getElementById(objectId).style;
    }
    else if (document.all && document.all(objectId)) {  
	return document.all(objectId).style;
    } 
    else if (document.layers && document.layers[objectId]) { 
	return document.layers[objectId];
    } else {
	return false;
    }
}
function switchDiv(div_id)
{
    var style_sheet = getStyleObject(div_id);
    if (style_sheet)
	{
	    hideAll();
	    changeObjectVisibility(div_id, "visible");
	}
    else 
	{
	    alert("Sorry, this only works in browsers that do Dynamic HTML");
	}
}