hmm would one of those PCI graphics cards play any decent games or is it a definate no no!?

I had a feeling my pc wasnt very upgrade-able but it seems abit stupid that its got a high GHz processor and room for upto 2 gigs of RAM yet it cant really play the top games because it cant house a decent graphics card!?

Im not too bothered to be honest because i dont really play much games and when i do im happy enough with my ps2 these days, and its a good job i think otherwise id be out buying a new pc