a:hover is correct, assuming you'll have links inside that div
If you're not bothered about Win/IE support, then you could use myelement: hover where myelement is the selector for the div you want. Give the div a class or an id or select it however you like.
If you are looking for Win/IE support, then you could use links, as Win/IE only supports the hover pseudoclass on links, rather than on any arbitrary element, like it should. Either that, or get funky with some JavaScript...