well that's up to you really, it would make it faster, you might have to get a new motehrboard that supports an 800MHZ FSB unless your's already does
if your motherboard doesn't support an 800MHZ FSB, and you do end up upgrading, I'd suggest you get an Athlon 64 3000+ in socket 939 and an Asus A8V or a Gigabyte motherboard
a good graphics card is anything from a 9600 upwards
you would prolly spend maybe $500 on those, and it should be much faster
I'm planning to get my own PC by the end of the year so I'm not stuck on the slow 500MHZ family PC