99 Cavalier 2.2 120k overheating

Hey guys Im new here in the Chevy scene, but anyway I did a few searches on this topic and need a expert opinion.
This is my g/f car by the way and you know how MOST girls are..they dont take care of their cars! Anyway, this past month or so she has been loosing a considerable amount of coolant, and I mean atleast 2-3 gallons a week. When I fill it up in the resevoir(sp?) there is the top of the resevoir where there is a whole and a tube coming out of it. This tube leads to nothing? Is it supposed to go anywhere? And now today it started overheating really bad, and I mean like smoke coming from engine(near the head) and down near the water pump. The water pump also looks very bad ( I mean bad like there is moisture and coolant all over it). Now as of right now the car is not being driven as it cannot because I dont want it overheating and causing more damage. What is the best way to fix this prob? Replacing the water pump, more then likely, right? But what else? I mean this looks bad here.

If its spraying coolant out near the waterpump, then you probably have a bad water pump. Simple, eh? So go buy you a new one and replace it accordingly. Oh yeah, don't worry about that rubber hose, if you look at the cap of your coolant resevoir, you'll see it looks like a thermostat. When the car overheats that cap responds appropriately and lets off some coolant. It prevents shit from exploding, its supposed to lead into emptiness.

How easy/hard is it to replace one? It looks like a bitch, also I found a used one on ebay for around 15usd, am I better off just buying a new one instead?
Thanks

well n/m about the purchase of one, I found a brand new one from Autozone for like 20 usd, now I just need to know how hard it is to put in.

I have a question about the water pump in a car. What does it EXACTLY do? Does it pump coolant from resevoir to engine and radiator? Is that why it is leaking so bad form the water pump, then thats why engines overheat? Am I correct? Also does anyone have any information on installing one of these!!

i put a water pump on my 89 cavalier z24 and it took an hour and a half tops

I have a new problem now. When I loostened the serpentine(sp?) belt by the tensioner screw, the belt came off fine. I didnt take the screw completley out. But now when I try to put the belt back on, that tensioner that the screw was on is pretty loose, like I can move it up and down with my hands. So when I try and tighten that screw again the belt wont get tight at all. Does anyone know whats wrong? Someone said that that tensione could be broke/bad. Is this possible? If so how would I fix this? Does anyone know what Im talking about? Thanks

I might be wrong but I don't think a belt tensioner can be fixed, only replaced.

I think you are having belt routed wrong way.You should have written it path down before taking it off.I have 1995 corsica and thing that your cavalier has same routing if it has A/C on it.Buy Cavalier book at any car store and look at the drawing.

Belt routing diagram should be on the underside of the hood I think.