ok so I bought a 98 cavalier z24 auto, and it runs rather well for as cheap as I got it for, however when i drive and get the rpm's up around 3k-4k rpm's the engine makes a chatter sound... I was told it was the timing chain..... can anyone tell me what it could be exactly?

Since you say it does it at high rpm's, try revving the engine by hand while listening for the rattle, try to localize it. If its at the front of the engine (passenger side), its almost definitely that chain. Do that and post back here what you find out.
Usually the timing chain would rattle at idle too, and its usually the timing chain tensioner that goes bad, not the chain itself, but then, once the tensioner craps out, the chain will deteriorate quickly, so if on further checking you figure out it IS the chain/tensioner, replace both at the same time.
And if you can swing the money at the same time, I would definitely think about replacing the waterpump also, as the 2.4 pump is a bear to change anyway, and you have access to it while doing the chain, so kill two birds with one stone. Even if the pump isn't bad, call it peace of mind that you have a pump good for another 100k miles or so.