Is vala a cross platform language?
You can easily port your Vala applications on Windows by two means:
- Run valac on Windows by using the mingw compiler on Windows
- Use mingw on Linux to cross-compile the generated C source for Windows
Both work very well, but I suggest to do the second because Vala on Linux is more up-to-date than on Windows.
If you mean "does it compile on Windows?", then see the "OS" section in the infobox on the right here: http://en.wikipedia.org/wiki/Vala_(programming_language) and here are the instructions: http://live.gnome.org/Vala/ValaOnWindows