Assigning each page with specific category

Hi,

I've create 3 page templates then I used the exact same code in theloop.php. Then I changes the lines 7 and 8:

global $post, $query_string;
query_posts($query_string);

To

global $post, $query_string;
query_posts(cat='4');

So now I have a page called: "Cars" With CategoryID = '4'

It works only for the first 10 posts, then pagination starts, the posts repeat them self. I know I'm doing something wrong in setting the "$query_string" , How can I assign that value to use category number '4' for this page.