Time to study...
http://auto.howstuffworks.com/disc-brake.htm
http://auto.howstuffworks.com/master-brake.htm
Pedal dropping to the floor, or mushy is a hydralic issue. Could be any number of things you mentioned, caliper, wheel cylinder (If you had drum brakes), master cylinder.
It probably ISN'T the brake booster since a failure there most likely would make the pedal harder to press, not easier.
Could be a rubber brake hose broken, a steel brake line ruptured, etc.
You will certainly need to get the wheels off and examine each caliper to see if there is fluid leaking anywhere. Then examine the master cylinder (this is under the hood where you put the brake fluid in the car) to see if it is leaking anywhere.
Inspect the brake lines, etc.
However, it sounds like some sort of hydralic system problem with a mushy pedal.
Good luck. I'd drive upstate to help, but I've got my daughter this weekend and I'm on call all next week. However, I'm a car junkie and like that sort of thing.
TB
