It's possible that some of the later 5900XT cards were based on the NV38 core instead of NV35. If that is the case with your card, it might explain why you are unable to use 45.23 drivers. Check what HWINFO says for the core.

BTW, I wouldn't worry too much about not being able to use 45.23. It's not the "end all be all" driver version for Win9x. I know of at least one game which doesn't work with it - Need for Speed 4: High Stakes. For that game, you either need driver version 30.82 or 56.64. None of the 4x.xx drivers will work with it.

It is NV35.
This fucking Windows ME does not work with nvidia drivers versions 4x.xx and older and it only works with nvidia drivers versions 5x.xx and newer!