Displaying categories in centre column

[amanuensis]

I have a category on the front page in the left column - when I click it the sub categories drop down, that's fine - when I click one of the sub categories the centre column exhibits the content of that sub category, so far so good - what I would like to do is this - when I click the category on the left column (not one of its sub categories) I would like to have the all the subcategories related to that category display in the centre. - ~Does anyone know how this can be done with PS 1.7

 

Any help would be more than appreciated.