In terms of training, there are plenty of veterans from Afghanistan that can teach them the use of these weapons, and they probably recieved training specific to this type of act (ie shoot as many as you can, go for important people's offices, don't go down without detonating yourself etc. etc.) and they were probably briefed on the layout of the building and nature of security etc.
However I seriously doubt that they recieved classic squad-style tactical training. That would take to long and the men that did this were disposable. Furthermore, that's not really the Taliban's style of fighting.