NT 5 would be Vista and earlier in this case, I believe. Specifying %LOCALAPPDATA% should be sufficient, though %USERPROFILE% (e.g. C:\Users\Steve) would also be okay.

%ProgramData% is not writable by limited users, but we don't want the global .ini to be editable by non-admin users. That said, even admins aren't supposed to go editing stuff in %ProgramData%, as I understand it.

I think having "alongside the EXE or in %LOCALAPPDATA%" is fine.