Hi Baz,
I played around a lot with the parameters and didn't really see much improvement of my images, but to answer your questions.....
Stacking Parameters....
1. See a recent DSS Yahoo message.....drizzle is only used when you are trying to put more detail into a small picture....I use it sometimes with my DSP Pro II on galaxies, but usually I don't use it...
2. RGB Align - this will align the R, G, B channels in the pic when using a DSLR or CCD one-shot....I don't bother as I usually mix the colours in PS or IRIS
Stacking Parameters - Light tab ....
I use Kappa Sigma clipping - 2 and 5....there is a tutorial on IRIS that explains Kappa Sigma stuff...
www.saratogaskies.com/articles/cookbook/index.html
High Dynamic Range stuff is for when you have something really dim and really bright...again, I never use it...maybe the pro's on this site know more here...
Cosmetic tab....
I do both hot and cold pixels - 1 and 50% ....again, I fiddled with it and just leave it at that now.....
Not sure if that is helpful, but as a bit of a novice, i just set it like that and not worry too much about it......for my DSLR pics, I sometimes use RGB Channels Background Calibration......
Alex