Şunu dener misin ?
<?php
$gel=$_GET['gel'];
$sql="SELECT * FROM Wallpapers where Category='$gel' ORDER BY RAND() LIMIT 5";
$sonuc=mysql_query($sql); var_dump(mysql_num_rows($sonuc));
$title=$sonuc["Title"];
$wallpaper=$sonuc["Wallpaper1"];
$id=$sonuc["ID"];
$seotitle = str_replace(" ", "+", $title);
echo "
<a href=\"/$seotitle/\"> $title </a><br>";
?>