Appearance & Action of Fly-Out Menu

Does anyone know which file to edit when making changes to the main category fly-out menu?

Also, I have a lot of sub-categories, but I only want to show the first level of fly-out categories. Otherwise the page starts looking a little too cramped.

How would I go about not having the 2nd and 3rd fly-out levels from showing (without labeling them as hidden- that defeats the purpose). I still want them to show up as drilldown options for the customer when they are in a main category.

Thanks for your help!