I found this very very interesting script by Adomas PaltanaviÄius to determine if you are using mousewheel.
It returns a delta value, +1 or -1, according to scroll direction.
I am publishing it here, and very soon I will start to use it to code games, form handlers, and so on.
Meanwhile, check the original script.
It needs some improvements due to some strange delta values on some browsers.
Scroll mouse wheel to see delta here.
Do you have an idea about how to use mouse wheel handling? Let me know, and I will (try to) code it.