To achieve a tabbed look you do not need to use the separators.
For the following HTML structure using NAV:

<dnn:NAV runat="server"
                            ID="dnnNAV"
                            ProviderName="DNNMenuNavigationProvider"
                            IndicateChildren="false"
                            ControlOrientation="Horizontal"
                            CSSNodeRoot="main_dnnmenu_rootitem"
                            CSSNodeHoverRoot="main_dnnmenu_rootitem_hover"
                            CSSNodeSelectedRoot="main_dnnmenu_rootitem_selected"
                            CSSBreadCrumbRoot="main_dnnmenu_rootitem_selected"
                            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" />

apply the following styles in your skin.css (please note that the following styles only draw the background images, and extra styles will be necessary to fully format your tabs):
.main_dnnmenu_rootitem span.txt   { display:inline-block; margin-right:XXpx; }
.main_dnnmenu_rootitem  { background: url('TABRIGHTIMAGE') no-repeat right; }
.main_dnnmenu_rootitem span.txt { background: url('TABLEFTIMAGE') no-repeat; display:block; height:YYpx; }

The purpose is making both spans (.main_dnnmenu_rootitem and .span_txt) overlap, except in width, where span_txt is smaller in width, so that rootitem displays the other corner of the tab.
Let me know if I didn't explain it clearly.

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Beatriz Oliveira
Founder of Bind New Media & Design and creator of Bind Tuning
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