I asked a few weeks ago about versions of Emacs for Windows
that might run on Itanium and/or AMD64 Windows, because the
elderly version we're using here doesn't work.
I just got a chance to try building 21.3 from the source kit.
I did this for plain x86, (rather than try to port all of Emacs
to the weird LLP64 data model that Win64 uses) and that starts
up and runs on both AMD64 and Itanium. The custom major mode we
use here doesn't work yet, but it's a step forwards. When we
have that working, we can think about moving all the ordinary
Windows users up to 21.3.