This module improves the :hover selector support in IE6 and 7. From the whatever:hover site:
Most modern browsers support the :hover selector for any html element. This is cool, because it enables you to, for instance, apply a mouseover effect to table rows
using only CSS. IE however, has an erratic support for :hover at best, depending on the particular version your visitor is using.
The module uses the file from that site too.