Here's the code:

<?php
/*
Penny Arcade RSS Feed Generator Script - Dynamically generates a feed for Penny Arcade
Copyright (C) 2005 Andrew Ferguson and "reklis"

This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.

*/
    header("Content-type: text/xml");
    echo "<?xml version=\"1.0\"?>";
?>
<rss version="2.0">
  <channel>
    <title>Penny Arcade Comics</title>
    <link>http://www.penny-arcade.com/view.php</link>
    <description>Most recent comics</description>
    <language>en-us</language>
    <?
        $today = strtotime(date("j F Y", time()));
        for($i=0; $i<21; $i++){
            $thisDay = $today-($i*86400);
            $thisDayOfWeek = date("D", $thisDay);
            if( ($thisDayOfWeek == "Mon") || ($thisDayOfWeek == "Wed") ||($thisDayOfWeek == "Fri")) {
            $title = "Comic for " . date("F jS, Y", $thisDay);
            $pubDate = date("r", $thisDay);
            $imgSrc = "http://www.penny-arcade.com/images/".date("Y/Ymd", $thisDay)."h.jpg";
            ?>
            <item>
                <title><?php echo $title; ?></title>
                <link><?php echo $imgSrc; ?></link>
                <description><![CDATA[
                    <img src="<?php echo $imgSrc; ?>" />
                    ]]>
                    </description>
                <pubDate><?php echo $pubDate; ?></pubDate>
            </item>       
            <?php
            }
        }
    ?>
  </channel>
</rss>