Yes, through CSS. Whilst you wouldn't be able to change a div to a circle, you could certainly remove the borders and do some magic with background images or other border tricks to change the overall shape to be something else.
EDIT: I may have been slightly wrong.
Well, I thought my colleague would post an witty retort to my declaration that ITS IMPOSSIBLE!
Anyway, since he hasn't, heres the code to make a circular div, magic!
border-radius: 50% 50% 50% 50%;
padding: 13%;
Apply this as you need to whatever divs you like, also probably also worth testing it across browsers.
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