Need help -Posts are showing in both parent and child categories

Coming Back to WP finally and getting back into it after a 4 month leave.

I used to use the Show Categories Plugin for 1.2 so that my post that were categorized in a sub category would not also show in the Parent.

But I upgraded to the latest 1.5.3. and the plugin doesn’t work.

What I have done on my site is this:
I made a template page that uses the wp_list_cats tag to show all my categories and sub categories on one page. When I click on the nested sub category link it goes to a (nicer) archive page with only listings of post titles that were assigned to that sub category.

Now when I go back to the Category Listing page and click on the Parent category link, all post titles of all sub categories show up in that listing as well.

How can I get it so that the posts titles will only show up in the sub category list?

Thanks for your help.

Randyd