Nissan Repair: Installing a knock and rear O2 sensors, haynes manual, o2 sensors

Question
Dear Von:
I have 99 Maxima that failed inspection due to emissions and the service engine soon light was on. Took car to service at the dealership, and was told the car needs a rear O2 and knock sensor. Also nees upper and lower intake gasket at a cost of almost $1200. I believe most of this cost is labor. Is there any way I can fix these items myself? If so, is it possible to get some sort of instruction on how to do this?
Your help is greatly appreciated. Thank you.  

Answer
Edward,

I see the upper intake gasket since it has to come off to get to the knock sensor.  But, I doubt that the lower one is needed unless you are leaking air from the lower gasket.  Purchase the parts and do it yourself.  You can get a Haynes manual that pretty much explains the process.  The rear oxygen sensor is easy.  Just purchase the oxygen sensor socket and a new oxygen sensor.  The knock sensor is not that difficult if you mark all the hoses and where they go.  If you have a digital camera that helps to document how things go back together adn get zip lock bagk to holt the parts and mark on the bag where they go.  The upper intake is easy since you are not tearing into the engine and only removing the upper intake.  The knock sensor is below so when the upper intake is off you can get to the sensor.  Replace it and put the intake back on with a new gasket.  Reset the codes and you are done.