I have a 2000 chev venture that has been sitting for 2-3 yrs thats been started once in a while but always killed the battery.

First.. Take your alternator to a parts store and have it tested. I am assuming you have not done a voltage check while it was running?If so, what was the voltage you were getting at idle? Also, you may want to check all ground wires for corrosion and/or connection. Also, as a warning.. Disconnecting the battery terminal while a computer controlled vehicle is running can damage the computer.

yes I checked all the grounds & cleaned them, that was my next step take alternator in have it check out, no I have not done a volt check. I was afraid the computer might be the problem, the lady who owned it before me said the motor blew a hose & sprayed coolant all over fuse box n battery. I was the one who replaced the blown hose after that she said it never ran right after that incident it always killed the battery. I checked everything made sure no exposed or positive wires not grounded out. Next options check alternator then computer will also check volts as u said....thanx for ur help

Alternator getting that wet could have shorted out the electronics and is causing it to stay on with the key off. Put something metal up to the shell while the car is off. If it is magnetized its deff the alternator.