the computer with the quad core uses pci express as a graphics card and the pentium 4 uses agp so i can't really change them
Then buy a faster card for the quad core. If you have about a 350 watt good power supply, a Radeon 6770 if you can find it or a 7750 if not at the lower end will work, for something a bit higher-end a 6790 will be a good match for the CPU, and will play games well above MW2 in graphics quality.
You have mismatched systems here, a faster video card with a much slower PC and a slow video card in a fast PC. Right now neither will run games well.