[javascript-dev] how to do sth like that?/javascript

Hi!
There is a nice feature that I've seen on data recovery services site.
When you move mouse over the "Country", in the top on the right side of the page, then the frame pop ups, 
with he list of country to choose. I want o do sth like that on my page, but I've just started to learn javascript, 
and I have no idea how to do it...can enybody help me out?
Here is a link to that site where I've seen these feature: http://www.salvagedata.com
Thank for your help.