Generally, things in the navbar, in the form of actual "buttons," go in the section which starts with:
Code:
<!-- nav buttons bar -->
For example, the first entry in a stock 3.6.8 navbar for this section is:
<table class="tborder" cellpadding="$stylevar[cellpadding]" cellspacing="0" border="0" width="100%" align="center" style="border-top-width:0px">
<tr align="center">
<if condition="$show['member']">
<td class="vbmenu_control"><a href="usercp.php$session[sessionurl_q]">$vbphrase[user_cp]</a></td>
</if>
<if condition="$show['registerbutton']">
<td class="vbmenu_control"><a href="register.php$session[sessionurl_q]" rel="nofollow">$vbphrase[register]</a></td>
</if>
This is the code for the "button" which appears on the far left of the navbar as "Register" if you are not logged in, and "UserCP" if you are logged in.
Unless you have Projects and/or Blogs installed, the next "stock" button would be:
Code:
<!-- <td class="vbmenu_control"><a href="faq.php?$session[sessionurl]" ">$vbphrase[faq]</a></td> -->
And so on across the list.
What you should notice, is that each entry has the following configuration: a reference to a .php file and a $vbphrase.
Code:
<td class="vbmenu_control"><a href="faq.php?$session[sessionurl]" accesskey="5">$vbphrase[faq]</a></td> -->
This one happens to be to the FAQ.
I would assume, without having seen your Arcade addon, that it would have similar language to add it's link to the navbar. This is just a sample, but probably looks something similar to your navbar code:
Code:
<td class="vbmenu_control"><a href="arcade.php$session[sessionurl_q]">$vbphrase[Arcade]</a></td>
Technically, I would believe you could put your navbar link to the Arcade in any position along the navbar that you want, as long as the <a href=" finds your php file for the Arcade and the $vbphrase listing contains the "text" which shows on the navbar.
You can adjust it's position shown on the navbar by where you place it among the existing code list of "buttons" already on the navbar.
Again, this is just general information on how the navbar is configured, without seeing the code for your Arcade plugin.
Hope that helps.
Regards,