Hooking up a monitor to a laptop

Hello,
I have an Alienware laptop and the screen is damaged because streaks started appreaing on it and then the left half of the screen went back and I can't get to my start menu or anything. So I got a Samsung 150s LCD monitor from someone which I have hooked up to my laptop, but I can't get it to work. When I boot up my laptop I can see the Windows XP screen on both monitors, but when once I get to the login screen the external monitor didn't show anything anymore. I have tried using the F3 button, but the external monitor says "video mode not supported". Does that mean I need Samsung driver? If so, where can I find a free one? Any help would be appreciated. Thanks!