Small change to Magento store navigation

Hi. I need a small change to my magento store drop down naviagtion. Currently I use a standard menu system, but I would like it changing so that the categories display in multiple columns rather than just one column. I know there are third party plugins for this, but they offer a lot more than I actually need. This should just be a change in a css file I think. Should be a two minute job for someone. Thanks