I think espeak as a sapi synth would be useful in windows. I'm learning Esperanto, and trying to read it using the english rules of most synths is quite annoying. I got it to compile under windows using mingw, but that was a while ago. I recall the only major problem was the fmemopen function, which I finally decided to take out, losing some functionality. It could still generate wave files from text files just fine though.
