Hehe... sounds familiar. Please download the latest beta of my Magyar Mod ("Ho ho ho..." in forums new civilizations section) and check whether there is the same effect. If there's not, then I can tell you what this is caused by. When I started playing and modding civ4, I had two rather weak machines (a laptop and a desktop pc). On both machines, I had the same problem, but noone else had. I figured out, that this was because I had animations deactivated in the menu for performance reasons while most other users had it actived as they had better machines. In this case, the same problem occurs that you describe. This can be fixed by copying the kfm and kf files to the modded units folder and make the reference in the xml file to there. Then, the freeze files of the original unit - which still contain the original units modell - don't get used and therefor the freeze mode (animations disabled) works again, although I guess that at least for those units, animations are still active (as there are no freeze files, right?). I pointed that out to the community several times, but nobody cared. Well, back then, animations could have been deactivated in the menu to solve this. But as this is not so obvious to less experienced users, I decided to deliver my mod with kf files dispite several modders wondered about that and even after I got a new machine some months ago (well, it's true that I haven't tested the units I have added since then, so theremight be some buggy ones there, too). Why Windows 7 forces freeze-mode (as it seems to me) - don't know...
The_Coyote once figured out how to create freeze nifs in a human way, although it still means work. Ask him, if you really need these files.