First of all, you need to determine if the water pump or thermostat is broken. That is more serious than a broken temperature gauge.
Warm up the engine. Heater and blower on high, is it hot? Yes, most probably thermostat stuck on closed.
If it is warm, most probably broken water pump.
Here is a post from Chongo. It highlights the ECT sensor.
The coolant temp gauge sender is the bronze (??) looking thing below the "Co" from the word coolant. Is that what you are talking about as the sender unit. If it is then if you do it real fast, unscrew and then plug (and screw) in the new one right away, you probably can get away with not having to drain the cooling system (according to Haynes). Haynes suggest to release the pressure by removing the coolant tank cap and then reinstalling the cap back (when the engine and coolant is completely cool). Hope this helps.
http://www.contour.org/ubbthreads/showflat.php?Cat=&Board=trouble&Number=983852&Forum=trouble&Words=chongo&Match=Entire%20Phrase&Searchpage=0&Limit=25&Old=allposts&Main=983239&Search=true#Post983852 
It went all the way over to the right(past the red off the scale) and hasn't moved in days. Does anyone know where the temperature sensor itself is located on the engine? Figured I'd start there and work my way up. Thanks