This is a very simplistic Fastpass explanation, but basically it works like this:
Anyone get a Fastpass, but you can only get one Fastpass at a time. You cannot get a Splash Mtn Fastpass and then immediately go get a HMH Fastpass. Once you get a Fastpass you can't get 2nd until the time of the 1st Fastpass.
With an AAA package (it must be a package w/lodging at one of the 3 DLR hotels) you get "Enhanced" Fastpass. With Enhanced Fastpass you can get more than one Fastpass at a time, for different rides. You can NOT get 2 Fastpasses for Splash, but could get one for Splash and one for HMH within minutes of each other.
Prior to 2004 AAA offered Enhanced Fastpass on any park tickets they sold, you did not have to get a package. Starting with 2004 you can only get the Enhanced Fastpass with a AAA package and the lodging MUST be at one of the 3 DLR hotels, not a good neighbor hotel.