Alian,
I had a similar issue with my Dell Vostro 3700 running a GeForce GT 330M (windows 7 Pro, 64 bit). When I first got it, the screen would flicker and get odd lines on start up, but stabilize after the log in screen came up. Updating my driver took care of the problem, it SHOULD fix your problem. Are you sure your downloading the correct driver (32 vs 64)? Make sure you download straight from [http://www.geforce.com/Drivers|nVidia]. Do you have your video settings set so that you are using your graphics card and not internal graphics?
Hope this helps!