Addictive Drums has an a section in it for mapping which is real easy to use.
I click the question mark in the upper right hand corner of AD2
I select Map Window drop down box on upper the left side
I click Empty under Map Preset Drop down box.
I click on a Kit piece in the Window and then select "learn" for the particular type of sound from that piece
I then click Learn for the kit piece and I then click the Pad on my Controller I want to assign for the kit piece and you will hear the Kit piece.
Continue for all Drum pieces you want assigned for the Drum Kit.
When done click SAVE under the Map Preset Drop Down box and give it a name.
You are done.
There is more in depth information but that's the basics for setting up a drum pad for AD2.
Groove3.com has a pretty good video Tutorial for using AD2 and Mapping to keys and pads.
See this
AD2 Mapping video as well on Youtube.com