If by 'Windows default reader program' you mean Narrator, the answer as far as we know has been so far: it depends on the version of Windows, but Narrator is basically crippled to use a limited selection from Microsoft. From a Wikipedia article:
"The Windows 2000 version of Narrator uses SAPI 4 and allows the use of other SAPI 4 voices. The Windows XP version uses the newer SAPI 5, however, it only allows the use of the default voice, Microsoft Sam, even if other voices have been installed. In Windows Vista, Narrator has been updated to use SAPI 5.3 and the Microsoft Anna voice, or the Microsoft Lili voice for Chinese systems."
[Link:
http://en.wikipedia.org/wiki/Microsoft_Narrator ]
Corrections welcome