ok, I am trying to use either the LM35 or lm335 sensor
but I see 2 different wiring diagrams for the sensor on different pages
http://guides.machinescience.org/mod/book/print.php?id=1348
says i need a 10k ohm resister with 1uF capacitor
http://mysite.du.edu/~etuttle/electron/elect23.htm
says I need i dont need anything 
Both of those are ways to wire up an LM35, but not an LM335. Read the datasheet. The cap and resistor act like low-pass filter and also probably lowers the impedance when the sensor is read. It would probably be more useful on long wiring situations to prevent oscillations.
I'm currently reading an LM34 using nothing but wires (no cap or resistor). It's a little noisy, but over-sampling it takes care of that. I think I'll try the cap and resistor and see if I can see any difference.
afremont:
Both of those are ways to wire up an LM35, but not an LM335. Read the datasheet. The cap and resistor act like low-pass filter and also probably lowers the impedance when the sensor is read. It would probably be more useful on long wiring situations to prevent oscillations.I'm currently reading an LM34 using nothing but wires (no cap or resistor). It's a little noisy, but over-sampling it takes care of that. I think I'll try the cap and resistor and see if I can see any difference.
thanks. but why is there 2 grounds for the first diagram? How do I connect them?
They just connect together and to the main system ground (GND) on the Arduiono. It's not uncommon for a schematic to have many parts connected to ground (Vss) or the positive supply (Vcc).
All those grounds are the same, connect them all together. That is just a style of doing the drawings
so that it doesn't have a lot of extra lines on the drawing leading to one ground point.