wordpress category display problem

Is there a way to display main category only.
and when main is clicked subcategory( if exists) comes in
and when a sub category is clicked all posts in that sub category are also displayed..

I repeat
1) only main category gets displayed
2) when main category is clicked sub category is displayed under it
3) under sub category all posts for that sub category are displayed

I don't know if it will do exactly what you want, but take a look at a plugin called "Fold Category List."