you might be able to get a bit off help, but I'm thinking it would be like putting shiny wheels on your car. Sure it will look better, but it really won't make it run much better
You'll basically be throwing money away. Any money you put into that computer will be a waste as you won't be able to use anything from it to upgrade into a newer system. Save your money, $500 will get you a decent system, $1000 will get you one of DrDeath's killer systems (do a search on these boards).