RE: Piezo film sensor interface
I can't give you the whole answer, but I can put you on the right track.
The sensor will give out a Charge for a known pressure.
The data sheet should tell you how many Pico Coulombs per unit of pressure the sensor will produce.
You already know that Q=VC (Charge = voltage * capacitance)
So if you feed a known Charge into a known Capacitance you can calculate the resulting voltage. Q/C = V
Beware that using the wrong kind of cable may have a large capcitance itself and could affect the signal.
What you are really looking for is a Charge Amplifier, (I have also heard of a constant current diode and a capacitor being used together but have no experience of doing this myself).
Hope this is a start for you.