The most easiest program you can use is DSS (deep sky stacker) free to boot
30 seconds isn't bad for Omega Centauri so what you need is about 30 subs
30 darks of equal length
and 30 flats(these don't need to be the same expsoure length)
for meanings etc I refer everyone too this link
http://www.saratogaskies.com/article...ook/index.html
Jim uses a program called Iris for stacking but I've used it and is long winded, I prefer DSS for its simplicity
In DSS you basic follow about 7 step (print the manual helps)
load lights(subs)
load darks
load flats
check all
registerd check pictures
click ok
click OK
and away it goes (you can change the parametres when you get used to the prcoess)
If you use ICNR you don't need darks and flats
Hope this helps
Cheers