Step one: remove the power supply in the computer and compare it to the 600W. Same size and design? If so, great. Next, look at the connectors, does the 600W have the same kind of connectors? If so, great.
The other issue is will the videocard physically fit. If you have a tower case this is good, it'll probably fit. You can look inside the case and see what kind of room you have. It'll take up two slots, and you need to make sure nothing is blocking the end of where it will go, so that a long card won't fit.