Embed a wiki page that already exists into the center column

I have my zencart installation in sub-directory “/store” , and my mediawiki installed in “/wiki”
I would like to have a link in the header that links to the main wiki page. (I know how to do this part) however I would like the wiki page to be displayed in the center column, not a new page.
Anyone have any idea the link should look like?
Link to a outside page example:
<?php if (DEFINE_FAQS_ALL_STATUS <= 1) { ?>
<li><?php echo '<a href=http://www.nmteaco.com/wiki/index.php?title=Tea>' . BOX_INFORMATION_TEA_INFO . '</a>'; ?></li>
<?php } ?>

Link to a Zencart page example:
<?php if (DEFINE_FAQS_ALL_STATUS <= 1) { ?>
<li><?php echo '<a href="' . zen_href_link(FILENAME_SITE_INFO, '', 'NONSSL') . '">' . BOX_INFORMATION_SITE_INFO . '</a>'; ?></li>
<?php } ?>

I just cant figure out how to combine them. So the outside page pops up in the center column.

Side note:
Does anyone know how to do a common login between mediawiki and zencart?