1) back-up your files
2) play around with home.html - add for example the string 123 on different places until you find out, where the right place is
That's all I can tell you now as long as I don't know if you use the default 4images template or not...
if it is the default template of 4i 1.7.1, then find this in home.html
{if categories}
and you may for example insert your php-file ABOVE that:
<table width="100%" border="0" cellspacing="0" cellpadding="3">
<tr>
<td class="row2" valign="top"><?php include(ROOT_PATH.'yourfilename.php'); ?></td>
</tr>
</table>
Yes, "yourfilename.php" has to be replace by the filename of the php-file you want to insert...