You hit the nail on the head. The buzzers are crap (though you could maybe take one apart to hack together an analog input for a phidget).
Most questions are answered here:
Parking Distance add on
Basically, there are two kits. Each kit is 4 sensors. One uses 4 wired sensors, and one uses 4 wireless sensors. Regardless of the kit, the sensors communicate with an interface box that is connected to the PC via USB.
The sensors are to be mounted (drilled) into the bumpers. 4 in the front, 4 in the rear.
In order to use two kits at the same time (front and rear), one must be wired and the other wireless.
As far as DriveLine is concerned, it's one of those things that just works. Programming the graphical part of it was a lot of fun.