Dark Frames

I have been experimenting with registax and my toucam.

I stacked a couple of thousand frames of M42 (through open window) and there
does indeed seem to be some nebula showing. I would like some advice on
these shots as there are several lines running down them. Any idea what this
is? I thought it might be noise but it seems a bit excesive. I will upload
them somewhere once I find a suitable place.

Anyhoo, I then read about Dark Frames, so I made one using about 200 frames
stacked. When I used this in Registax it deleted most of the detail in the
shot so I was only left with two or three stars (greatly dimmed)and no
nebula. I have thought about this and have come to the following conclusion
and would like advice as to where I am wrong:

Registax applies my dark frame to each frame individually (rather than the
finished stack) so I should probably be using a dark frame which is made of
either one frame or a small number. What is the best number? Or am I
completely wrong?
Also, when making the dark frame, is it important to have the camera
settings the same as when capturing the image of the star etc?

Regards,

Stuart