A common problem in Magento is the lack of an import / export program in Magento. One of the solutions is importing / exporting directly to the MySQL database, but there is a nice plugin as well, made by user Santhosh, well known from the Magento Commerce Forum.
Install the plugin by uploading it to your webdir. In the admin, a menu Santhosh will appear. You can run it now in order to import/export. The category sheet will appear in the following CSV format.