I found the pinout for Nellcor DS-100A sensor as :
pin1,4,6,8 : NC (in fact between pin 1 and 6 of the sensor is 7.5k resistor)
pin 2 : red wire; anode of the IR LED, cathode of the red LED
pin 3: black wire; cathode of the IR LED, anode of the red LED
pin 7 : cable shield, connects to copper shield over the phototransistor
pin 9 : phototransistor cathode
pin 5 : phototransistor anode, white wire; phototransistor detects level of IR and/or red light transmitted through the finger
I was able to use the leds, but stuck in getting signal out of the sensor. (I have connected pin 5 to Vdd (5V) through a pull-up transistor (since its the phototransistor), but I couldn't get the signal out at that pin (I just get a constant voltage around 0.47V). Anybody give me a hint to get the signal out from the sensor......Thanks alot.