Hi
You need to include the CategoryID from your categories table in the query...
Try something like this:
mysql_select_db($database_PowerCMSConnection, $PowerCMSConnection);
$query_Category = "SELECT CategoryID, CategoryName, products.ProductCategoryID FROM productcategories INNER JOIN products ON ProductCategoryID = CategoryID";
$Category = mysql_query($query_Category, $PowerCMSConnection) or die(mysql_error());
$row_Category = mysql_fetch_assoc($Category);
$totalRows_Category = mysql_num_rows($Category);