It depends on where you want the googlecheckout button displayed. I have mine outside of the form at the end of the page like this:
<tr>
<td><?php echo tep_draw_separator('pixel_trans.gif', '100%', '10'); ?></td>
</tr>
<tr>
<td><table border="0" width="100%" cellspacing="1" cellpadding="2" class="infoBox">
<tr class="infoBoxContents">
<td><table border="0" width="100%" cellspacing="0" cellpadding="2">
<tr>
<td width="10"><?php echo tep_draw_separator('pixel_trans.gif', '10', '1'); ?></td>
<td align="left" td class="main"><?php echo tep_image_submit('button_update_cart.gif', IMAGE_BUTTON_UPDATE_CART); ?></td>
<?php
$back = sizeof($navigation->path)-2;
if (isset($navigation->path[$back])) {
?>
<td class="main" align="right"><?php echo '<a href="' . tep_href_link($navigation->path[$back]['page'], tep_array_to_string($navigation->path[$back]['get'], array('action')), $navigation->path[$back]['mode']) . '">' . tep_image_button('button_continue_shopping.gif', IMAGE_BUTTON_CONTINUE_SHOPPING) . '</a>'; ?></td>
<?php
}
?>
</tr>
</table></td>
</tr>
</table></form></td>
</tr>
<tr>
<td>
<?php
// *** BEGIN GOOGLE CHECKOUT ***
if (defined('MODULE_PAYMENT_GOOGLECHECKOUT_STATUS') && MODULE_PAYMENT_GOOGLECHECKOUT_STATUS == 'True') {
include_once('googlecheckout/gcheckout.php');
}
// *** END GOOGLE CHECKOUT ***
?>
</td>
</tr>
<?php
} else {
?>
<tr>
<td align="center" class="main"><?php new infoBox(array(array('text' => TEXT_CART_EMPTY))); ?></td>
</tr>