One way to do this is to have two child
divs in the container
div. One should be
img1 and the other should contain the other three, which should also have
display: block; to work properly (img1, img2 and img 3).
float: left; on
float: right on the
container of the three smaller ones.
To be on the safe side, put again on both
img1 and the new
If the containers also have fixed dimensions it'll be even easier.