Look in includes -> Templates -> YOUR_TEMPLATE -> common -> tpl_header.php
find:
Code:
<table border="0" cellspacing="0" cellpadding="0" class="headerNavigation" align="center">
<tr class="headerNavigation">
<td align="left" valign="top" width="247" class="headerNavigation"><a href="<?php echo zen_href_link(FILENAME_DEFAULT, '', 'NONSSL'); ?>"><?php echo HEADER_TITLE_CATALOG; ?></a> |
<a href="<?php echo zen_href_link(UN_FILENAME_WISHLIST, '', 'SSL'); ?>">Wish List</a> |
<?php if ($_SESSION['customer_id']) { ?>
<a href="<?php echo zen_href_link(FILENAME_LOGOFF, '', 'SSL'); ?>"><?php echo HEADER_TITLE_LOGOFF; ?></a> |
<a href="<?php echo zen_href_link(FILENAME_ACCOUNT, '', 'SSL'); ?>"><?php echo HEADER_TITLE_MY_ACCOUNT; ?></a>
<?php
} else {
if (STORE_STATUS == '0') {
?>
<a href="<?php echo zen_href_link(FILENAME_LOGIN, '', 'SSL'); ?>"><?php echo HEADER_TITLE_LOGIN; ?></a>
</td>
<td align="center" width="220">
</td>
<td class="headerNavigation" align="right" valign="top" width="291">
</td>
The portions in red are fixed width try changing them to percentages.
Make the first one 50% and the other 2 at 25%.
See if that helps