New installation - cannot increase the screen resolution

[Chan Lee]

Hi,
   
  I just installed Debian using DVD set from CheapBytes
  into a new HP Pavilion Slimline s3020n desktop. It has
  Nvidia GeForce 6150LE graphics adaptor driving 1280x1024
  resolution.
   
  Thrying to increase the screen resolution using the Screen
  resoultion preference tool, however, I cannot find any extra
  resolution option in the menu - only the basic resolution of
  640x480 is available. The Samsung 19inch LCD screen can
  display 1280x1024 - how can I increase it ?
   
  Thanks for your help in advance,
   
  Chan