WARNING: The output is not 100mV ... 150mV. It is a bridge sensor. The 100mV ... 150mV is the difference between the output pins. Since the sensor needs 12V the output pins are near 6V, and this is too high for the Arduino.
ADVICE: Buy an other pressure sensor. Look at the sites of Sparkfun and Adafruit to see what kind of pressure sensors can be used with the Arduino. You first have to know if you want a baromic, absolute pressure sensor or a relative pressure sensor.
OPAMP: If you want to use this sensor, you have to use an opamp. But you have to use a good regulated 12V for the sensor and a good 5V for the Arduino. Opamps like the INA128 can be used as opamp. I think they operate at a low voltage like 5V and allow the inputs to be a higher voltage.
This is a simular pressure sensor : http://playground.arduino.cc/Main/SPX3058D
That pressure sensor uses 5V, which is okay for the Arduino. By connecting it directly to the Arduino inputs, the calculated pressure is very inaccurate. But the sensor was inaccurate anyway, so it was still usable for me.