Versions of PowerPoint before PowerPoint 2007 did not had the ribbon interface. In order to mimic the functionality provided by the ribbon interface on older versions, a "custom ribbon window" has been provided for these older versions.
The "ribbon" on PowerPoint 2003 and earlier versions
To show the "ribbon", or hide it again when it is showing, click on the PowerMerge button of the PowerMerge toolbar or the PowerMerge menu item on the standard Tools menu.
PowerMerge toolbar
Power merge item on the Tools menu