That graphics card requires a 330w or higher power supply. Considering that the OEM unit inside that system is below recommended spec, is pretty old at this point (And likely cannot sustain even the capacity it was able to when new, much less the capacity requirements of the graphics cards recommendations) and almost certainly wasn't a terribly great unit to begin with, I'd be pretty doubtful that you're going to have a problem free situation there.
That being said, you can certainly try it, but I suspect you'll have problems and it may not even be particularly safe given the age of the power supply.