check /themes/yourtheme/theme.php for $template_gallery_admin_menu
if you don't have it already copy it from sample/theme.php to your theme then change it the way you want to
here is an example:
I want to add a button call My admin tools to the menu right after config button:
$template_gallery_admin_menu = <<<EOT
<div align="center">
<table cellpadding="0" cellspacing="1">
<tr>
<!-- BEGIN admin_approval -->
<td class="admin_menu" id="admin_menu_anim"><a href="editpics.php?mode=upload_approval" title="{UPL_APP_TITLE}">{UPL_APP_LNK}</a></td>
<!-- END admin_approval -->
<td class="admin_menu"><a href="admin.php" title="{ADMIN_TITLE}">{ADMIN_LNK}</a></td>
<!-- BEGIN My_admin_tools -->
<td class="admin_menu"><a href="myadmintools.php" title="My admin tools">My admin tools</a></td>
<!-- END My_admin_tools -->
<td class="admin_menu"><a href="catmgr.php" title="{CATEGORIES_TITLE}">{CATEGORIES_LNK}</a></td>
<td class="admin_menu"><a href="albmgr.php{CATL}" title="{ALBUMS_TITLE}">{ALBUMS_LNK}</a></td>
<td class="admin_menu"><a href="groupmgr.php" title="{GROUPS_TITLE}">{GROUPS_LNK}</a></td>
<td class="admin_menu"><a href="usermgr.php" title="{USERS_TITLE}">{USERS_LNK}</a></td>
<td class="admin_menu"><a href="banning.php" title="{BAN_TITLE}">{BAN_LNK}</a></td>
<td class="admin_menu"><a href="reviewcom.php" title="{COMMENTS_TITLE}">{COMMENTS_LNK}</a></td>
<!-- BEGIN log_ecards -->
<td class="admin_menu"><a href="db_ecard.php" title="{DB_ECARD_TITLE}">{DB_ECARD_LNK}</a></td>
<!-- END log_ecards -->
<td class="admin_menu"><a href="picmgr.php" title="{PICTURES_TITLE}">{PICTURES_LNK}</a></td>
<td class="admin_menu"><a href="searchnew.php" title="{SEARCHNEW_TITLE}">{SEARCHNEW_LNK}</a></td>
<td class="admin_menu"><a href="util.php" title="{UTIL_TITLE}">{UTIL_LNK}</a></td>
<td class="admin_menu"><a href="profile.php?op=edit_profile" title="{MY_PROF_TITLE}">{MY_PROF_LNK}</a></td>
<!-- BEGIN documentation -->
<td class="admin_menu"><a href="{DOCUMENTATION_HREF}" title="{DOCUMENTATION_TITLE}" target="cpg_documentation">{DOCUMENTATION_LNK}</a></td>
<!-- END documentation -->
</tr>
</table>
</div>
EOT;
check the <!-- BEGIN My_admin_tools -->....<!-- END My_admin_tools --> block