If you get a new graphic card on the first computer such as 6850 you will be able to run it perfectly, but as the guy above me said if you take the card from the second computer and put it in the first one you should be getting a very good preformence, not maximum graphic, but very playable FPS while using good graphics.
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.