windsurfer - Get Em Fast would have to advise on that, as it would probably involve the jQuery effects.

Loter - To get hover effects on the higher items in the tree, find in your stylesheet_categories_menu.css the rule like this
Code:
#nav-cat li a:hover {
   color: #FFFFFF;
   background-color: #000000;
}
and add a rule above it to get this
Code:
#nav-cat li:hover>a {
   color: #FFFFFF;
   background-color: #a00000;
}

#nav-cat li a:hover {
   color: #FFFFFF;
   background-color: #000000;
}
Adjust properties to fit your situation.