You've got the same processor I had in my old computer that served me 4 years. P4 Northwood core. Anyways, 512 is kind of skimpy. I would probably stick another 1 gig in the system. I think what allowed me to keep that system that long was the fact that I had 1.5gb of ram in it. You'll notice a nice performance boost when you add in some ram. Especially if you're coming from 512mb.
Adding the ram will give u the benefit of seeing a nice overall system boost. Programs will start up faster, windows will boot faster, and you can have more multitasking going on at once. Ram is also cheap right now.
The video card would also help, but AGP cards are becoming more rare and actually more expensive than their PCI-E counterpart because not many companies make them anymore and the in the numbers they used to be made.
