Speech recognition is using your voice to control the computer. Older versions of Office included speech recognition, but now this feature is a part of Windows.
To set up speech recognition, go to the instructions for your version of Windows:
If your operating system is Microsoft Windows XP, you must run a previous version of a Microsoft Office system program to use speech recognition features.
Are you looking for Text-to-speech? See How to configure and use Text-to-Speech in Windows XP or Hear text read aloud with Narrator.
Excel has text-to-speech functionality built in to the program. To use text-to-speech commands in Excel, see Converting text to speech in Excel.