CSS Positioning

Hello, I've been experimenting with css, particularly trying drop down menus.
I'm a bit confused on the positioning aspect, ie: how do i keep the text links
in the nav from going down to the next line when the browser window shrinks?

My testing page is at: http://www.elapsedepoch.com/dropdown_test.html
and my css is at: http://www.elapsedepoch.com/styles/dropdown.css

Thanks, I'm really eager to be better friends with css!