Menu - submenu drop - PHP ?

[mysterio2099]

I'm not sure what to call this idea, or even what language is used to make it. I've only seen it on one website...i think it was isohunt.com or something like that... But, what it is:

When a link is clicked (it was on their search results) this box (submenu) drops down under it showing all kinds of extra information.

I wanna know how to make that drop down type menu. I can't remember if it droped over the links below it, or moved them all down and filled the space between....I'll take either way, as that part doesn't matter for the website I'm wanting to use it on.

If anyone can help, please do.

Thanks

(i have attached an animated .gif showing an example)

[mysterio2099]

and, another example could be the menu here on PCmech... when you hit "search" up top, it drops down a menu, or when you click "quick links" ...anything the the down arrow..........