First off the question should be : Should I do it ?

to give you some background , I am creating a site that will have 5 main categories , I am using the Tabs to get to these , once in the chosen Cat I would like the categories box to only show the next level of Sub Categories for that Top level Category.

Do you think this would go against ease of use ? or would it make it easier ?

If so , can someone point me in the right direction to start hiding the top level cats on demand.

Thanks for any input on the subject.