Also, if you've already installed AD2 (using the XLN installer, of course) you have to hit "Register" again and scroll down to select AdPaks and Kit Pieces. You can also select the MIDIPaks, but I had better luck doing that after using my browser to log onto the XLN website.
And whatever you do, don't touch the "Get Deal" button again. Once you've made your selections, go back to the Install window. Kit Pieces and AdPaks will show up and you can hit the "Update" button (it make be called something else, but that's close) to install.
I hit an error while trying to get the MIDIPaks through the XLN installer and that may be why they never showed up in the install list. Just keep in mind that you may have to log onto the XLN website to get them.