I have an hp slimline compact pc and i want to put a better video card in it what will fit in this small area?

i have 1 open free pci slot available i am running a nvidia video card now and i want to stay with this brand but i want to put a 8500 gt card in it but not sure if it will fit..does anyone know of a video card that i can can put inside this case.will a slimline card fit or do i need to buy a bigger case. please help me if possible|||slimline should fit, and getting a larger case will allow for more possibilities. check the size and type of card that is currently installed and go with that same sort, if its built-in then its more complicated.,