Im fairly new to PHP so there might be better ways to do what you want, but this is what I came up with, its nothing great and might be a little buggy but im giving you something to start with not a complete script. This script will not work if register_globals is off or if the webserver is on windows.. if register_globals is off it wont take much editing to make it work, and I can do that for you..
Create a blank file called file.txt and set the permissions to 666
file.php
$file = file_get_contents("file.txt");
$file2 = explode("|", $file);
echo "<img src=\"$file2[0]\">";
echo "<br>";
echo $file2[1];
add.php
echo "<form action=\"add1.php\" method=\"post\">
<input type=\"text\" name=\"link\">
<input type=\"text\" name=\"desc\">
<input type=\"submit\">
</form>";
add1.php
$open = fopen("file.txt","w");
$data = $link . "|" . $desc;
fwrite($open, $data);
fclose($open);
echo "Image and description added";
good luck!