Toshiba Sattelite L305-S5907 Gaming?

I downloaded COD4 Demo to mess around with the settings, and it runs OK on low settings, I can deal with it until I can save up enough money for an ASUS laptop. Everything passes on 'Can You Run It?' except for my graphics card, which is a Mobile Intel(R) 4 Series Express Chipset Family, which I don't know what it is but it sounds horrible. How much would a better graphics card be? Would it be worth it to put one in? Can I even do that on this laptop?

TOSHIBA Satellite C645D-S4024 Notebook AMD Athlon II Dual-Core P320(2.10GHz) 14" 3GB Memory 250GB HDD 5400rpm DVD Super Multi ATI Radeon HD 4250

TOSHIBA Satellite L655-S5156WH NoteBook Intel Pentium P6200(2.13GHz) 15.6" 4GB Memory DDR3 1066 320GB HDD 5400rpm DVD Super Multi Intel HD Graphics

TOSHIBA Satellite L655D-S5066RD NoteBook AMD Turion II Dual-Core P520(2.3GHz) 15.6" 4GB Memory 320GB HDD 5400rpm DVD Super Multi ATI Radeon HD 4250

TOSHIBA Satellite L645D-S4100 Notebook AMD Athlon II Dual-Core P360(2.30GHz) 14" 3GB Memory DDR3 1066 320GB HDD 5400rpm DVD Super Multi ATI Radeon HD 4250