installing web cam problems on vista

When i try to install my pentax camera as a webcam using the CD rom that came
with the camera, it automatically opens an installer based on the old windows
MX kind of interface. Then a windows vista pop up comes up, asking for a
file stream.sys. the thing is that it won't find it although it is actually
there in the windows-system32-drivers folder. I don't understand why it won't
find it and install it.

Is it perhaps because of this administrator window coming up constantly? i
am the only user and administrator of this computer, i fear that somehow this
type of protection that comes with vista messes up with installing new
software or drivers.

Any help?