Categories & Sub Categories (not displaying sub cats)

Hi All
OK i'm having an issue with categories and sub categories.
Im new at this so dont know if its something i'm doing wrong or if its a conflict between marketpress and my theme.
i would like to have what i would class as a standard layout on my shop where if a category has sub categories, then if you open that category, it logically and automatically shows you the sub categories, rather than only displaying all the products within those sub categories, which is what is happening with my site at the moment.

please take a look at....
http://www.pcperfect.co/store/

i have created a simple table with my main categories. for example if you click on the networking link, it takes you to the networking category, which has 2 sub cats, ADSL & DSL, yet it does not display these, only the products within the 2 sub cats. Why is it doing this????????
if this is norm, it kind of defeats the object of having sub cats, or am i doing something wrong??????

PLEASE HELP
many thanks