This simple plugin installs into your 1.5 site to blacklist or whitelist IP addresses and ranges for either the administrator or the site. The settings can be used interchangeably so the administrator can be set to white list mode and the site can be set to black list mode.

Read more at: http://extensions.joomla.org/component/option,com_mtree/task,viewlink/link_id,4201/Itemid,35/