SymVoc requires Microsoft .net framework 3.5 - it's included in Windows Vista and can be installed in Windows XP from here.
For speech synthesis it can use a SAPI compatible synthesiser or a custom product called Expressivo - more information in walk-through Documentation demo.
Zip archive with SymVoc binaries:
SymVoc_en_binaries.zip
Source code:
SymVoc_sources.zip