I have a good 2005 year PC (HP d4100Y: 3 GB RAM, 3.0 GHz Dual Core CPU, 400 watt PSU) GeForce 6600 video card (PCIe), and 19 inch high end CRT monitor. So far it all has performed very well, and with newer games like Team Fortress 2 and Half-Life 2 it performs quite well.
But on latest games...