How to replace speed sensor on 2000 Nissan Quest

Hi all,
Looks like I need to replace the speed sensor on my 2000 Nissan Quest. Periodically the speedometer will stop measuring speed and drop to zero, then it will pick back up measuring current speed. Seems to happen when I drive for more than 20 or 30 mins.
How would I replace this sensor? Also, is there any chance of damage if I don't replace the sensor in a timely fashion?
Thanks,
Ed

Replace Speed Sensor
Replace the speed sensor. It is around $85.00 to $110.00. I bought mine at my local Nissan dealer for $85.00 while the local Autozone had it for $110.00, figure that. That will fix the speedometer issue. You have to lift the car to get access to the sensor from underneath the engine. It is at the far back side of the transmission at the center of the car. Easy to find.
speed wire
have the same problem. i hope some one have an idea.
yea, i downloaded the pdf
yea, i downloaded the pdf files from another nissan site
i did the transmission scan & confirmed my sensor, or the plastic drive gear, is going bad
now in limp mode & can't go faster than 50 mph
search other threads on this site; i already added my inputs there
we might just need the speedometer pinion if the sensor is ok...
http://www.courtesyparts.com/quest-parts-v41-1998-2002/genuine-nissan-parts/power-train/327-speedometer-pinion/-c-5063_5064_5129_5138.html
part # 32703
confirmed bad vss...
... i replaced it awhile ago and speedometer and odometer now works just like new!
it was a ford part and the pinion gear was ok; i just transferred it over to the new sensor, lube the o-ring with some ATF, and installed it