Да уж
Самый элементарный способ через temp-переменную..
$sql="SELECT prop_name,value
FROM properties,prod_values,products
WHERE
prod_id = product AND
prop_id = property AND
prod_cat_id = 1
ORDER BY prop_id, prod_id";
$result = mysql_query ($sql);
$temp = "";
while($row = mysql_fetch_array($result) )
{
$prop_name = ($temp != $row[\'prop_name\']) ? $temp=$row[\'prop_name\'] : "";
$prop_name = $row[\'prop_name\'];
$values = $row[\'value\'];
echo "
".$prop_name." | ".$values." |
";
}