The first thing I see is your opening tag, you have <php? where it should be <?php
The second thing I see is that you could do things a little easier...
Code:
<?php
$banner_array = array(
'Sunday' => 'http://www.japamor.com/banners/ferrocash/sfs/200x250_001.gif',
'Monday' => 'http://www.japamor.com/banners/ferrocash/sfs/200x250_002.gif',
'Tuesday' => 'http://www.japamor.com/banners/ferrocash/sfs/200x250_003.gif',
'Wednesday' => 'http://www.japamor.com/banners/ferrocash/sfs/200x250_004.gif', 'Thursday' => 'http://www.japamor.com/banners/ferrocash/sfs/200x250_005.gif',
'Friday' => 'http://www.japamor.com/banners/ferrocash/sfs/200x250_006.gif',
'Saturday' => 'http://www.japamor.com/banners/ferrocash/sfs/200x250_001.gif'
);
$today = date("l");
?>
html here
<p>
<img src="<?php echo $banner_array[$today];?>">
Not that I particularly like that solution -- I would probably write a quick cron job to copy the right banner into place. Alternatively, you could consider using phpadsnew which would allow you to do all sorts of banner management.