How can I pop up a element from a website into a windows with Greasemonkey?

I want to pop up an image or a div/class from a website into a window with Greasemonkey, how can I do it?

For example, I want to pop up the stackoverflow logo to a small window (the size of the logo) when I enter the site.

I think you'll want to use window.open, which will open a new window whose size you can dictate.