Oh, my bad - I was working on the assumption that test_msvc9compiler was
testing compiler related stuff, so obviously would have the compiler
installed.  But it makes sense you might test support for that compiler
on a machine other than the one doing the building.

As for ProductId, Windows 7 has that under the "Windows NT" key instead
of "Windows".  My XP systems seem to have it in both places.  Don't know
about earlier Windows versions.

If it's something for general use, how about HKCU\Control
Panel\Desktop\DragFullWindows (REG_SZ, but should be 0 or 1).  Everyone
should have desktop settings.  It's on both my XP and Win7 systems. 
Looking around at http://www.pctools.com/guides/registry/ would seem to
indicate that key should be present on all releases back to Win95,
though some other web references make it unclear if the key is
automatically there on Win9x.  I can do some quick test installs to
verify if I get a moment tonight though.

Alternatively, you could just pick something for Windows 7 and let any
other platform default back to the old Notepad key, perhaps fixing the
error message to suggest running Notepad?  It's not like anyone else has
complained about the test failing before this, and it's only Windows 7
for which running Notepad the first time won't create the necessary key.

I suppose checking for the desktop key first, and falling back to the
notepad key would accomplish the same thing without having to check
platform.

-- David

PS: Have we hit our "ridiculous amount of effort expended against such a
small item" quota yet?  :-)