Same problem here. The wonky mouse acceleration is severely hampering my enjoyment of the game.
I feel lucky compared to the folks who can't even install/play the game at all, but it's still plenty frustrating to not be able to hit what you need to hit because the bizarre and inconsistent mouse input.
A couple of notes:
Editing "Default.ini" doesn't work. Default.ini is only used the first time the game starts up, or after it crashes. The game settings are usually read from Bioshock.ini, which is located in your user directory.
With Vista it's located in C:\Users\<your username>\AppData\Roaming\Bioshock
With XP, I think it should be in C:\Documents and Settings\<your username>\AppData\Roaming\Bioshock (I don't have XP)
That being said, Changing CaptureMouse to False did nothing for me, as did tweaking all the ReduceMouseLag options, etc.
The most effective thing I've done is by editing "User.ini", found in the same directory as Bioshock.ini. The mouse speed is set in several instances of the same lines:
MouseX=IF_MOUSE_LOOK_ENABLED Count bXAxis | IF_MOUSE_LOOK_ENABLED Axis aMouseX Speed=2500.0
MouseY=IF_MOUSE_LOOK_ENABLED Count bYAxis | IF_MOUSE_LOOK_ENABLED Axis aMouseY Speed=2500.0
You can do a global search-and-replace of
which will slow the movement to a more reasonable speed. However, it doesn't make the acceleration any less terrible, and in fact, may make it more noticable because when it's slow, it's REALLY slow.
It's really disappointing that there is clearly so much attention to detail in the game, yet the developers shrugged off one of the most fundamental elements of a PC first person shooter -- responsive mouse input.
We should be spending our effort fighting the splicers, not fighting the controls. It ruins the immersion.