[Halcyon]

Well you can probably upgrade the ram quite cheaply.
There may be a way where you would add more RAM and more of it could be shared to handle the onboard graphics, but you are not going to notice a great difference.

if you have a spare PCI port you could stick in a new grpahics card and disable the onboard one, but you would be looking at a low end model as your system would probably not support the latest graphics cards.

You could hunt around to see if there are better drivers for the graphics adapter but I doubt it will do much.

The problem is that if you uipgrade one thing, you will be limited by another, in your case the CPU and RAM.

There comes a time when your PC becomes only useful for browsing the net and E-mailing, or playing the retro game from the old days and thats where you are now.
Upgrading would probably cost money that wouldnt be a good investment as you'd find you'd belimited again later on.
You can get a good system that will play games for about £500 now.