CSS left and right aligning

In a navbar I want 4 images on the left and 1 image to align to the right of
the window. As the user resizes the window the right image should always be on
the right, EXCEPT when it touches the other 4 images on the left, then the
image should stop.

While I can float an image to the right, then it slides under (or over, I
forget) the left images. This is not what I want to happen. I know how I could
do it with tables, but any ideas how to do this with CSS?