When the installer is finished copying packages, it will probe for a mouse and inform you of the results. It then presents a list of choices for which mouse configuration to use, select the one which is most appropritate to your situation. If you have a two-button mouse, make sure to check the "Emulate 3 Buttons" box-this allows you to simultaneously click both buttons to emulate a middle button click.
The installer will now attempt to detect your video hardware. If it doesn't detect your card, you will be presented with a list to choose from.
Now you must tell the installer about your monitor. If your monitor isn't in the list, dig out the manual for it and select custom. You will need to know the maximum resolution, and the vertical sync range of your monitor. If you aren't sure, use conservative values.
The installer will now attempt to determine the best mode for your monitor by probing the graphics hardware. You can either accept the default it determines or select a mode you prefer.