Customize Category Pages to Display Subcategories

Hi all, We need to display the subcategories in a list format on the parent category pages. I've manually done this in one page but would like to eliminate the need as our category tree grows and changes frequently. [login to view URL] Also, this is done using a two column table. I've also tried some wrapping tricks using CSS in order to keep it as one list so it is visible on a mobile phone. So the two parts of this project will include: Automatically populating the sub-categories on its parent page(s) Displaying the subcategories in 2 columns on a PC but 1 column for phone