constrained div proportions in fluid layout

I have a div container that i want to resize with the browser to a max/min width and height.

Let's say the maximum width is 960px and the minimum is 500px.

How can I have the height of this div adjust and constrain the dimensions with CSS?

Is it possible? My CSS skills go out the window when I have to start playing with percentages and ratios..

Also, my element is centered in the browser, adn I don't want the browser width to be the same as the element before the resizing begins - ie, I would like there to be always right and left margin.