if you take a look at a previous question

http://stackoverflow.com/questions/2690742/mod-rewrite-title-slugs-and-htaccess

I am using the solution that Col. Shrapnel proposed- but when i assign values to $_GET in the actual file and not from a request the code doesnt work. It defaults away from the file as if the $_GET variables are not set

The code I have come up with is-

if(!empty($_GET['cat'])){

    $_GET['target'] = "category";


    if(isset($_GET['page'])){

        $_GET['pageID'] = $_GET['page'];

    }

    $URL_query = "SELECT category_id FROM cats WHERE slug = '".$_GET['cat']."';";
    $URL_result = mysql_query($URL_query);
    $URL_array = mysql_fetch_array($URL_result);

    $_GET['category_id'] = $URL_array['category_id'];



}elseif($_GET['product']){

    $_GET['target'] = "product";


    $URL_query = "SELECT product_id FROM products WHERE slug = '".$_GET['product']."';";
    $URL_result = mysql_query($URL_query);

    $URL_array = mysql_fetch_array($URL_result);
    print_r($URL_array);

    $_GET['product_id'] = $URL_array['product_id']; 

The original variable string that im trying to represent is

/cart.php?Target=product&product_id=16142&category_id=249

And i'm trying to build the query string variables with code and including cart.php so i can use cleaner URL's

So I have product/product-title-with-clean-url/ going to slug.php?product=slug

Then the slug searches the db for a record with the matching slug and returns the product_id as in the code above.Then built the query string and include cart.php