The Cakewalk Command Center does not install AD2. The Addictive Drums installer for SONAR Producer contains an rtf file called XLN_Audio_Addictive_Drums_Installation_Instructions_CC.rtf
The short version is you need to go the the XLN Audio site, create an account if you do not have one, download and install the XLN installer. Then use the AD2 code provided in your SONAR account (it is also displayed in the Command Center when this item is selected) to redeem your producer pack. One redeemed select and install 3 ADPaks, 3 MIDIPaks and 3 Kit pieces.