Just put one wire to GND, the other to pin 2 (external interrupt 0) with a pullup resistor (10k should be OK) to 5V.Then use the example code from attachInterrupt() (http://arduino.cc/it/Reference/AttachInterrupt). You have to register the time difference between two pulses (use micros() for that) and calculate the frequency from that.
Just wondering what you meant by a pull up resistor?
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