[G33K]

I believe most flex sensors, if not all, act as variable resistors giving analog values. In this way, you'd wire the flex sensor into one of the analog inputs on the Arduino. The Arduino has an analog-to-digital converter on-board and you can program it to "write" those values through the USB port via serial interface. If for some reason you are unable to or don't want to use the 0-1023 numerical values the Arduino reads from the analog ports, you can always map them to different values or really do whatever you want with them.