Make sure the hard drive is at least 7200RPM and not one of the old 5400RPM. There will be a painfully noticeable speed difference between them.
Also make sure your power supply is large enough to handle a new video card, 550watt + perhaps? With stats as low as your post, I'd expect a ~300watt supply which won't run newer video cards. Also check the amp rails too, some video cards require higher than normal ones. I'd bought a nice 700 watt supply that didn't work since it didn't put out enough amps.
