Drop down categories

Hi! Quick question. Is there any way to place my categories as pages in the header with drop down menus? I've seen a lot of other sites with this, and when I ask they all tell me it is part of their theme already. I would love to move my themes to the header rather than as a side widget, and preferably I'd be able to split them up (one for my travel parent category with a drop down, one for my teaching english abroad parent category etc.) Is there any way to do this? Thanks so much! My site is www.adventuresaroundasia.com