For all people where this tutorial not went because (the button won't shown in the bar), here is a code, i used it by the SMF 1.1.4 in the German version.
its all the same but the php code is alrady a litle bit different!
// SMFShop
echo ($current_action == 'shop' || $context['browser']['is_ie4']) ? '' : '' , '
<li class="mainNav-shop"><a href="', $scripturl, '?action=shop">',$txt['shop'],'</a></li>' , $current_action == 'shop' ? '' : '';
Sorry for my mispronunciation but I normaly speak german !!