Microsoft Agent uses SAPI 4.0 to provide speech services. Windows XP however now ships with SAPI 5.0 which does not provide backward compatibility support for its predecessor. Fortunately, SAPI 4.0 and SAPI 5.0 can co-exist together on the same Windows XP computer.
In order for the speech engines to work with Microsoft Agent in Windows XP, the SAPI 4.0 runtime support is also required to be installed already.