What resolution .ico files do XP and Vista show on the desktop?

There's loads of choices for .ico files but I can't see any logic in how Windows chooses which resolution/bit depth to show

From stackoverflow Jan Bannister

• There are the sizes of icons I bundle, which is the union of all the sizes you may need for XP and Vista depending on the settings the user chooses:

  • 16x16
  • 22x22
  • 24x24
  • 32x32
  • 40x40
  • 48x48
  • 64x64
  • 96x96
  • 128x128
  • 256x256
  From Nick

• It chooses the best bit-depth your display can handle, and the icon size is a system setting stored in SystemInformation.IconSize.

  From Jon Grant