Over the last few years, OpenOffice.org has started to develop a respectable number of extensions, mostly for Writer and Calc, the two most widely used applications. The OpenOffice.org Extensions site lists only a handful that are unique to Impress. The recently released eVoice, which records sounds for direct insertion into a slide, is one of them. Once configured, eVoice is straightforward to learn, and becomes even more useful when you're working with other Impress features.
Before you can use eVoice, you need Java installed. The free IcedTea version that comes with Fedora will do, but the GCJ version that comes with Debian will not. For basic use, you also need a microphone that works with your system. Once you have met these basic requirements, download eVoice from the OpenOffice.org extension site and install it using Tools -> Extension Manager. After that, you'll have an eVoice menu and a new floating tool bar with a single icon.