Thanks for your help.

I don't have it on a live site, so I can't post a link, but I can post the source of the page and my css classes.  I modified the DNN menu provider to assign my own css classes and that's how the classes with the background images get assigned.

Here's how I have the DNN Nav:

<dnn:NAV runat="server" ID="dnnNAV" ProviderName="UCUMenuNavigationProvider" IndicateChildren="false"
                            ControlOrientation="Horizontal"
                            CSSContainerSub="main_dnnmenu_submenu" CSSNodeHoverSub="main_dnnmenu_itemhover"
                            CSSNodeSelectedSub="main_dnnmenu_itemselected" CSSContainerRoot="main_dnnmenu_container"
                            CSSControl="main_dnnmenu_bar" CSSNode="main_dnnmenu_bar" CSSBreak="main_dnnmenu_break" />
                    </div>

Notice I removed the following:

CSSNodeRoot="main_dnnmenu_rootitem" CSSNodeHoverRoot="main_dnnmenu_rootitem_hover"
                            CSSNodeSelectedRoot="main_dnnmenu_rootitem_selected" CSSBreadCrumbRoot="main_dnnmenu_rootitem_selected"

I did that because i didn't want those classes overriding mine.

In my provider I add the proper css classes at the node level.

Here's the source of a page where I have the Home tab selected:
Notice the css class assigned to the Home menu item:   homeSelected

<input name="__dnnVariable" type="hidden" id="__dnnVariable" value="dnn_dnnNAV_ctldnnNAV_xml&lt;root id=dnn_dnnNAV_ctldnnNAV>&lt;n bcrumb=1

selected=1 id=36 key=36 txt= ca=3 url=http://localhost/dnn490/Home/tabid/36/Default.aspx cssHover=homeHover cssIcon=  cssSel=homeSelected>

&lt;n id=56 key=56 txt=TestPage2 ca=3 url=http://localhost/dnn490/TestPage2/tabid/56/Default.aspx cssIcon=  />&lt;/root>SearchIconWebUrlurl(/DNN490/images/Search/google-icon.gif)SearchIconSiteUrlurl(/DNN490/images/Search/dotnetnuke-icon.gif)SearchIconSelectedS" />

Here's my css classes:
.homeHover
{
 background-image: url(nav_Home_on.gif);
 height: 32px;
 width: 100px;
}

.homeSelected
{
 background-image: url(nav_Home_active.gif);
 height: 32px;
 width: 100px;
}

.TestPage1Normal
{
 background-image: url(nav_Networks.gif);
 height: 32px;
 width: 200px;
 background-attachment: fixed;
 background-repeat: no-repeat;
}

Finally, here's the folder structure (it's the default dnn structure under default folder)

DNN490\Website\Portals\_default\Skins\MinimalExtropy/index.asx -- that's the skin

DNN490\Website\Portals\_default\Skins\MinimalExtropy/css/menu.css  -- classes are in this file, images are in this folder.

That's what the DNN Menu uses to indicate the css selected class for that node.  That html was generated by the menu provider.  So it shows the correct class is assigned (the other attributes of the css class show up so I know it is using that class), but the background image is not appearing.  I'm wondering if it's because an actual hyperlink control is used in the menu?  You can't assign background images to hyperlink controls in ASP.NET.  I'm thinking Jon Henning would know how this works, or someone on the menu team?