Edit the header of WPG2 output page

Hi all,
I'm wondering which is the exact file which i have to edit in order to customize the header of my WPG2 output page.
This is the generated code that i'd like to edit(don't know if it helps too much) :

<table bordercolor="#FFFF33" border="2" width="100%">
<tr><div id="content" class="g2_column">

<div id="gallery" class="gecko">
<div id="gsHeader">
<a href="/~42-wip/?page_id=11"><img src="/~42-wip/gallery2/images/galleryLogo_sm.gif"
width="107" height="48" alt=""/></a>
</div>
<div id="gsNavBar" class="gcBorder1">
<div class="gbSystemLinks">
<span class="block-core-SystemLink">
<a href="/~42-wip/?page_id=11&amp;g2_view=core.SiteAdmin&amp;g2_return=%2F%7E42-wip%2F%3Fpage_id%3D11%26g2_e_id%3D11%26g2_wpg2_returnurl%3Dhttp%253A%252F%252Fnegrila.info%252F%257E42-wip%26g2_wpg2_returnname%3DFriends%2B%2526%2BCo">Site Admin</a>
</span>

but the problem is that i don't know which and where is the function which generates this code.

Thanks a lot.