Hi,
M42 is a difficult object because of the range. Most people take different length shots to bring out the different details.
Say 15 to 30 sec for the core. Then 2 minutes for the inner nebulosity then 3 to 5 minutes for the outer nebulosity. They then combine these images using HDR techniques and get a full dynamic range without the blown out core.
As a starter just wack the images into DSS and use the HDR option and see what you get
As far as darks are concerned DSS allows you to select the darks you want processed at the beginning. It then creates a master dark and applies this.
There are probably far better ways of doing this but for a beginner like me I usually let DSS handle all the details.
The attached image of M42 is stacked in DSS. I forget know but i think it was 2 by 30 sec, 2 by 1 minute and 2 by 5 minutes. One 30 sec dark, 2 1 minute darks and 2 5 minute darks all thrown into DSS. Stacked using HDR option, saved without adjustments, then processed in CS2. I dont pretend it is a great image but more of example of what can be done in DSS.