I think it might depend on the distro (the detection I mean). Some can add
something to the list as "other," even if they don't know what it is. Others
might look for an active NTFS partition and assume Windows, I don't know. In
any case, it's way easier to add it after the fact. I'm not sure what
management tools Ubuntu uses, but in SuSe, it's cake. If that fails, as
you've been told, editing the menu.lst file ought to do the trick.