Instructions
Click "Start" then "All Programs" and click "Grand Theft Auto IV."
Click "Settings."
Click "Video Mode"
Click "Resolution."
Change the resolution to your desired value. Your screen will change and you will see a message asking you if you would like to keep this resolution.
Click "Yes." to change your resolution. If you selected a resolution your hardware does not support, do nothing for 10 seconds and your prior resolution will be loaded. Your screen will turn black if you selected a resolution unsupported by your PC.