I think it's being actively developed on OSX and
Linux with a
Windows port
The lead developers do seem to use mostly Linux and OS X, but because
they are using a cross platform toolkit (wxwindows) I don't think
it's really a big deal to create the Windows binary for each release.
If you're interested I suggest you join the audacity-user mailing list
on sourceforge - it's friendly and helpful.
Cheers
Daniel