The idea of the Text-to-Speech feature is to type the voice-over narration in the Slide Notes panel and have Captivate convert it to a sound clip. To convert typed text to sound clips, Captivate uses some pre-installed voice packages called speech agents.
Due to their very large size, Adobe decided to make the installation of the Text-to-Speech agents optional. Captivate 7 ships with one voice-package that installs several speech agents for various languages.
The speech agents of Captivate can be downloaded from the following locations:
http://www.adobe.com/go/Cp7_win32_voices_installer (for Windows 32 bit)
http://www.adobe.com/go/Cp7_win64_voices_installer (for Windows 64 bit)