Update 2/17/11: After March 11, 2011 the Static FBML application will no longer be available. It will continue to work on existing custom tabs but all new tabs will need to be created with Iframes. Please see my tutorial on how to create a custom Facebook page tab with Iframes.
People often ask how to rename the page tabs on their facebook fan pages. Unfortunately, this functionality does not currently work. Facebook used to have this feature but it hasn’t worked since the last update.
You can, however, use the fbml application to create a custom box that is used as a tab. The tab will be whatever you name it, such as Welcome or Services, and that tab will contain whatever data you included in that fbml box.