Your Magento folder does not have sufficient write permissions, which this web based downloader requires.

If you wish to proceed downloading Magento packages online, please set all Magento folders to have writable permission for the web server user (example: apache) and press the "Refresh" button to try again.

To learn more about setting write permissions, please visit the Magento community site for further details.

Alternatively, if you are a developer and familiar with SVN, you can follow these instructions to check out the latest Magento branch.